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 $30.93   9.671%   $33.9212   $33.92   $33.90   $33.90  
  Purchase #2 $95.62   3.145%   $98.6272   $98.63   $98.65   $98.60  
  Purchase #3 $190.64   5.641%   $201.394   $201.39   $201.40   $201.40  
  Purchase #4 $119.30   12.123%   $133.7627   $133.76   $133.75   $133.80  
  Purchase #5 $98.47   3.414%   $101.8318   $101.83   $101.85   $101.80  
  Purchase #6 $180.50   3.332%   $186.5143   $186.51   $186.50   $186.50  
  Purchase #7 $66.83   7.717%   $71.9873   $71.99   $72.00   $72.00  
  7 purchase totals = $782.29       $828.0385   $828.03   $828.05   $828.00