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 $195.26   13.559%   $221.7353   $221.74   $221.75   $221.70  
  Purchase #2 $24.53   8.643%   $26.6501   $26.65   $26.65   $26.70  
  Purchase #3 $201.51   5.872%   $213.3427   $213.34   $213.35   $213.30  
  Purchase #4 $12.85   7.733%   $13.8437   $13.84   $13.85   $13.80  
  Purchase #5 $119.36   12.156%   $133.8694   $133.87   $133.85   $133.90  
  Purchase #6 $162.45   13.522%   $184.4165   $184.42   $184.40   $184.40  
  Purchase #7 $69.50   12.836%   $78.421   $78.42   $78.40   $78.40  
  7 purchase totals = $785.46       $872.2787   $872.28   $872.25   $872.20