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 $62.87   8.172%   $68.0077   $68.01   $68.00   $68.00  
  Purchase #2 $166.75   5.376%   $175.7145   $175.71   $175.70   $175.70  
  Purchase #3 $12.94   12.616%   $14.5725   $14.57   $14.55   $14.60  
  Purchase #4 $247.55   6.239%   $262.9946   $262.99   $263.00   $263.00  
  Purchase #5 $6.44   9.450%   $7.0486   $7.05   $7.05   $7.00  
  Purchase #6 $223.62   13.857%   $254.607   $254.61   $254.60   $254.60  
  Purchase #7 $91.93   4.760%   $96.3059   $96.31   $96.30   $96.30  
  7 purchase totals = $812.10       $879.2508   $879.25   $879.20   $879.20