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 $58.77   4.772%   $61.5745   $61.57   $61.55   $61.60  
  Purchase #2 $26.38   3.134%   $27.2067   $27.21   $27.20   $27.20  
  Purchase #3 $17.37   13.254%   $19.6722   $19.67   $19.65   $19.70  
  Purchase #4 $144.34   5.680%   $152.5385   $152.54   $152.55   $152.50  
  Purchase #5 $180.58   8.344%   $195.6476   $195.65   $195.65   $195.60  
  Purchase #6 $13.76   12.608%   $15.4949   $15.49   $15.50   $15.50  
  Purchase #7 $235.53   8.266%   $254.9989   $255.00   $255.00   $255.00  
  7 purchase totals = $676.73       $727.1333   $727.13   $727.10   $727.10