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 $59.48   5.872%   $62.9727   $62.97   $62.95   $63.00  
  Purchase #2 $75.84   4.457%   $79.2202   $79.22   $79.20   $79.20  
  Purchase #3 $182.38   6.443%   $194.1307   $194.13   $194.15   $194.10  
  Purchase #4 $70.47   10.730%   $78.0314   $78.03   $78.05   $78.00  
  Purchase #5 $236.90   4.474%   $247.4989   $247.50   $247.50   $247.50  
  Purchase #6 $131.25   7.487%   $141.0767   $141.08   $141.10   $141.10  
  Purchase #7 $7.76   7.494%   $8.3415   $8.34   $8.35   $8.30  
  7 purchase totals = $764.08       $811.2721   $811.27   $811.30   $811.20