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 $227.66   8.322%   $246.6059   $246.61   $246.60   $246.60  
  Purchase #2 $237.78   5.698%   $251.3287   $251.33   $251.35   $251.30  
  Purchase #3 $87.75   5.346%   $92.4411   $92.44   $92.45   $92.40  
  Purchase #4 $61.33   11.535%   $68.4044   $68.40   $68.40   $68.40  
  Purchase #5 $188.62   13.624%   $214.3176   $214.32   $214.30   $214.30  
  Purchase #6 $52.85   7.267%   $56.6906   $56.69   $56.70   $56.70  
  Purchase #7 $205.96   7.396%   $221.1928   $221.19   $221.20   $221.20  
  7 purchase totals = $1,061.95       $1,150.9811   $1,150.98   $1,151.00   $1,150.90