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 $192.74   12.742%   $217.2989   $217.30   $217.30   $217.30  
  Purchase #2 $245.55   8.649%   $266.7876   $266.79   $266.80   $266.80  
  Purchase #3 $49.75   10.250%   $54.8494   $54.85   $54.85   $54.80  
  Purchase #4 $41.49   12.803%   $46.802   $46.80   $46.80   $46.80  
  Purchase #5 $13.78   13.138%   $15.5904   $15.59   $15.60   $15.60  
  Purchase #6 $66.75   13.686%   $75.8854   $75.89   $75.90   $75.90  
  Purchase #7 $75.46   12.329%   $84.7635   $84.76   $84.75   $84.80  
  7 purchase totals = $685.52       $761.9772   $761.98   $762.00   $762.00