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 $236.29   11.871%   $264.34   $264.34   $264.35   $264.30  
  Purchase #2 $57.71   9.821%   $63.3777   $63.38   $63.40   $63.40  
  Purchase #3 $202.98   5.404%   $213.949   $213.95   $213.95   $213.90  
  Purchase #4 $24.25   12.655%   $27.3188   $27.32   $27.30   $27.30  
  Purchase #5 $250.71   10.460%   $276.9343   $276.93   $276.95   $276.90  
  Purchase #6 $68.45   6.772%   $73.0854   $73.09   $73.10   $73.10  
  Purchase #7 $6.84   7.352%   $7.3429   $7.34   $7.35   $7.30  
  7 purchase totals = $847.23       $926.3481   $926.35   $926.40   $926.20