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 $201.46   11.827%   $225.2867   $225.29   $225.30   $225.30  
  Purchase #2 $85.41   9.512%   $93.5342   $93.53   $93.55   $93.50  
  Purchase #3 $237.26   5.462%   $250.2191   $250.22   $250.20   $250.20  
  Purchase #4 $121.43   8.811%   $132.1292   $132.13   $132.15   $132.10  
  Purchase #5 $124.26   10.637%   $137.4775   $137.48   $137.50   $137.50  
  Purchase #6 $107.42   11.450%   $119.7196   $119.72   $119.70   $119.70  
  Purchase #7 $226.71   13.351%   $256.9781   $256.98   $257.00   $257.00  
  7 purchase totals = $1,103.95       $1,215.3444   $1,215.35   $1,215.40   $1,215.30