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 $30.68   6.610%   $32.7079   $32.71   $32.70   $32.70  
  Purchase #2 $105.95   12.549%   $119.2457   $119.25   $119.25   $119.20  
  Purchase #3 $41.52   13.429%   $47.0957   $47.10   $47.10   $47.10  
  Purchase #4 $69.53   4.327%   $72.5386   $72.54   $72.55   $72.50  
  Purchase #5 $174.57   7.562%   $187.771   $187.77   $187.75   $187.80  
  Purchase #6 $187.67   7.522%   $201.7865   $201.79   $201.80   $201.80  
  Purchase #7 $87.79   11.863%   $98.2045   $98.20   $98.20   $98.20  
  7 purchase totals = $697.71       $759.3499   $759.36   $759.35   $759.30