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 $69.38   10.587%   $76.7253   $76.73   $76.75   $76.70  
  Purchase #2 $142.97   9.497%   $156.5479   $156.55   $156.55   $156.50  
  Purchase #3 $146.70   9.301%   $160.3446   $160.34   $160.35   $160.30  
  Purchase #4 $180.53   7.612%   $194.2719   $194.27   $194.25   $194.30  
  Purchase #5 $26.39   12.272%   $29.6286   $29.63   $29.65   $29.60  
  Purchase #6 $194.44   7.204%   $208.4475   $208.45   $208.45   $208.40  
  Purchase #7 $125.61   3.683%   $130.2362   $130.24   $130.25   $130.20  
  7 purchase totals = $886.02       $956.2020   $956.21   $956.25   $956.00