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 $34.46   4.622%   $36.0527   $36.05   $36.05   $36.10  
  Purchase #2 $119.64   4.694%   $125.2559   $125.26   $125.25   $125.30  
  Purchase #3 $108.38   6.839%   $115.7921   $115.79   $115.80   $115.80  
  Purchase #4 $232.77   11.273%   $259.0102   $259.01   $259.00   $259.00  
  Purchase #5 $194.89   10.803%   $215.944   $215.94   $215.95   $215.90  
  Purchase #6 $112.44   4.224%   $117.1895   $117.19   $117.20   $117.20  
  Purchase #7 $60.34   7.544%   $64.892   $64.89   $64.90   $64.90  
  7 purchase totals = $862.92       $934.1364   $934.13   $934.15   $934.20