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 $66.78   12.681%   $75.2484   $75.25   $75.25   $75.20  
  Purchase #2 $203.28   12.617%   $228.9278   $228.93   $228.95   $228.90  
  Purchase #3 $230.39   13.278%   $260.9812   $260.98   $261.00   $261.00  
  Purchase #4 $23.99   4.630%   $25.1007   $25.10   $25.10   $25.10  
  Purchase #5 $211.71   7.401%   $227.3787   $227.38   $227.40   $227.40  
  Purchase #6 $97.92   3.264%   $101.1161   $101.12   $101.10   $101.10  
  Purchase #7 $35.58   4.755%   $37.2718   $37.27   $37.25   $37.30  
  7 purchase totals = $869.65       $956.0247   $956.03   $956.05   $956.00