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 $182.54   9.146%   $199.2351   $199.24   $199.25   $199.20  
  Purchase #2 $69.97   6.748%   $74.6916   $74.69   $74.70   $74.70  
  Purchase #3 $98.94   6.484%   $105.3553   $105.36   $105.35   $105.40  
  Purchase #4 $231.65   7.652%   $249.3759   $249.38   $249.40   $249.40  
  Purchase #5 $65.81   9.763%   $72.235   $72.24   $72.25   $72.20  
  Purchase #6 $234.28   8.312%   $253.7534   $253.75   $253.75   $253.80  
  Purchase #7 $107.46   11.457%   $119.7717   $119.77   $119.75   $119.80  
  7 purchase totals = $990.65       $1,074.4180   $1,074.43   $1,074.45   $1,074.50