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 $51.55   12.547%   $58.018   $58.02   $58.00   $58.00  
  Purchase #2 $89.56   9.479%   $98.0494   $98.05   $98.05   $98.00  
  Purchase #3 $221.68   6.791%   $236.7343   $236.73   $236.75   $236.70  
  Purchase #4 $106.27   5.747%   $112.3773   $112.38   $112.40   $112.40  
  Purchase #5 $48.92   4.694%   $51.2163   $51.22   $51.20   $51.20  
  Purchase #6 $77.66   9.216%   $84.8171   $84.82   $84.80   $84.80  
  Purchase #7 $153.79   4.226%   $160.2892   $160.29   $160.30   $160.30  
  7 purchase totals = $749.43       $801.5016   $801.51   $801.50   $801.40