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 $55.43   3.249%   $57.2309   $57.23   $57.25   $57.20  
  Purchase #2 $246.92   13.388%   $279.9776   $279.98   $280.00   $280.00  
  Purchase #3 $221.95   3.758%   $230.2909   $230.29   $230.30   $230.30  
  Purchase #4 $162.69   8.604%   $176.6878   $176.69   $176.70   $176.70  
  Purchase #5 $115.62   8.410%   $125.3436   $125.34   $125.35   $125.30  
  Purchase #6 $67.75   12.383%   $76.1395   $76.14   $76.15   $76.10  
  Purchase #7 $20.44   9.182%   $22.3168   $22.32   $22.30   $22.30  
  7 purchase totals = $890.80       $967.9871   $967.99   $968.05   $967.90