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 $110.49   8.164%   $119.5104   $119.51   $119.50   $119.50  
  Purchase #2 $13.82   11.587%   $15.4213   $15.42   $15.40   $15.40  
  Purchase #3 $176.92   3.356%   $182.8574   $182.86   $182.85   $182.90  
  Purchase #4 $149.48   8.353%   $161.9661   $161.97   $161.95   $162.00  
  Purchase #5 $97.40   7.133%   $104.3475   $104.35   $104.35   $104.30  
  Purchase #6 $44.95   5.310%   $47.3368   $47.34   $47.35   $47.30  
  Purchase #7 $109.94   10.562%   $121.5519   $121.55   $121.55   $121.60  
  7 purchase totals = $703.00       $752.9914   $753.00   $752.95   $753.00