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 $186.63   12.617%   $210.1771   $210.18   $210.20   $210.20  
  Purchase #2 $161.76   11.537%   $180.4223   $180.42   $180.40   $180.40  
  Purchase #3 $240.99   8.146%   $260.621   $260.62   $260.60   $260.60  
  Purchase #4 $164.39   5.421%   $173.3016   $173.30   $173.30   $173.30  
  Purchase #5 $99.77   3.859%   $103.6201   $103.62   $103.60   $103.60  
  Purchase #6 $108.63   9.874%   $119.3561   $119.36   $119.35   $119.40  
  Purchase #7 $46.96   4.341%   $48.9985   $49.00   $49.00   $49.00  
  7 purchase totals = $1,009.13       $1,096.4967   $1,096.50   $1,096.45   $1,096.50