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 $92.42   3.847%   $95.9754   $95.98   $96.00   $96.00  
  Purchase #2 $132.63   4.701%   $138.8649   $138.86   $138.85   $138.90  
  Purchase #3 $127.57   4.522%   $133.3387   $133.34   $133.35   $133.30  
  Purchase #4 $14.60   12.465%   $16.4199   $16.42   $16.40   $16.40  
  Purchase #5 $250.31   6.664%   $266.9907   $266.99   $267.00   $267.00  
  Purchase #6 $63.38   4.393%   $66.1643   $66.16   $66.15   $66.20  
  Purchase #7 $112.86   12.659%   $127.1469   $127.15   $127.15   $127.10  
  7 purchase totals = $793.77       $844.9008   $844.90   $844.90   $844.90