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 $14.39   5.323%   $15.156   $15.16   $15.15   $15.20  
  Purchase #2 $64.63   13.330%   $73.2452   $73.25   $73.25   $73.20  
  Purchase #3 $58.46   3.138%   $60.2945   $60.29   $60.30   $60.30  
  Purchase #4 $219.99   10.524%   $243.1417   $243.14   $243.15   $243.10  
  Purchase #5 $176.58   6.393%   $187.8688   $187.87   $187.85   $187.90  
  Purchase #6 $14.99   3.684%   $15.5422   $15.54   $15.55   $15.50  
  Purchase #7 $159.95   4.738%   $167.5284   $167.53   $167.55   $167.50  
  7 purchase totals = $708.99       $762.7768   $762.78   $762.80   $762.70