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 $6.74   13.199%   $7.6296   $7.63   $7.65   $7.60  
  Purchase #2 $87.87   5.332%   $92.5552   $92.56   $92.55   $92.60  
  Purchase #3 $14.63   4.294%   $15.2582   $15.26   $15.25   $15.30  
  Purchase #4 $187.79   4.185%   $195.649   $195.65   $195.65   $195.60  
  Purchase #5 $132.92   6.533%   $141.6037   $141.60   $141.60   $141.60  
  Purchase #6 $88.54   8.389%   $95.9676   $95.97   $95.95   $96.00  
  Purchase #7 $204.29   13.727%   $232.3329   $232.33   $232.35   $232.30  
  7 purchase totals = $722.78       $780.9962   $781.00   $781.00   $781.00