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 $39.93   3.874%   $41.4769   $41.48   $41.50   $41.50  
  Purchase #2 $191.26   8.175%   $206.8955   $206.90   $206.90   $206.90  
  Purchase #3 $105.36   13.583%   $119.671   $119.67   $119.65   $119.70  
  Purchase #4 $85.71   7.327%   $91.99   $91.99   $92.00   $92.00  
  Purchase #5 $67.59   12.464%   $76.0144   $76.01   $76.00   $76.00  
  Purchase #6 $144.51   10.452%   $159.6142   $159.61   $159.60   $159.60  
  Purchase #7 $127.67   3.773%   $132.487   $132.49   $132.50   $132.50  
  7 purchase totals = $762.03       $828.1490   $828.15   $828.15   $828.20