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 $154.85   12.523%   $174.2419   $174.24   $174.25   $174.20  
  Purchase #2 $25.79   13.420%   $29.251   $29.25   $29.25   $29.30  
  Purchase #3 $209.56   3.142%   $216.1444   $216.14   $216.15   $216.10  
  Purchase #4 $144.34   9.432%   $157.9541   $157.95   $157.95   $158.00  
  Purchase #5 $49.47   12.249%   $55.5296   $55.53   $55.55   $55.50  
  Purchase #6 $226.82   12.748%   $255.735   $255.74   $255.75   $255.70  
  Purchase #7 $73.62   5.312%   $77.5307   $77.53   $77.55   $77.50  
  7 purchase totals = $884.45       $966.3867   $966.38   $966.45   $966.30