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 $124.53   4.594%   $130.2509   $130.25   $130.25   $130.30  
  Purchase #2 $125.63   10.849%   $139.2596   $139.26   $139.25   $139.30  
  Purchase #3 $48.89   8.794%   $53.1894   $53.19   $53.20   $53.20  
  Purchase #4 $82.38   11.546%   $91.8916   $91.89   $91.90   $91.90  
  Purchase #5 $245.75   12.427%   $276.2894   $276.29   $276.30   $276.30  
  Purchase #6 $218.51   7.438%   $234.7628   $234.76   $234.75   $234.80  
  Purchase #7 $94.39   3.836%   $98.0108   $98.01   $98.00   $98.00  
  7 purchase totals = $940.08       $1,023.6545   $1,023.65   $1,023.65   $1,023.80