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 $88.53   7.521%   $95.1883   $95.19   $95.20   $95.20  
  Purchase #2 $129.66   5.395%   $136.6552   $136.66   $136.65   $136.70  
  Purchase #3 $241.85   5.564%   $255.3065   $255.31   $255.30   $255.30  
  Purchase #4 $44.79   5.213%   $47.1249   $47.12   $47.10   $47.10  
  Purchase #5 $51.38   7.856%   $55.4164   $55.42   $55.40   $55.40  
  Purchase #6 $237.89   10.523%   $262.9232   $262.92   $262.90   $262.90  
  Purchase #7 $84.56   3.253%   $87.3107   $87.31   $87.30   $87.30  
  7 purchase totals = $878.66       $939.9252   $939.93   $939.85   $939.90