Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.87   13.174%   $232.9913   $232.99   $233.00   $233.00  
  Purchase #2 $170.55   6.544%   $181.7108   $181.71   $181.70   $181.70  
  Purchase #3 $113.42   7.110%   $121.4842   $121.48   $121.50   $121.50  
  Purchase #4 $190.53   11.798%   $213.0087   $213.01   $213.00   $213.00  
  Purchase #5 $250.83   10.563%   $277.3252   $277.33   $277.35   $277.30  
  Purchase #6 $108.30   11.729%   $121.0025   $121.00   $121.00   $121.00  
  Purchase #7 $146.95   5.301%   $154.7398   $154.74   $154.75   $154.70  
  7 purchase totals = $1,186.45       $1,302.2625   $1,302.26   $1,302.30   $1,302.20