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 $226.86   11.655%   $253.3005   $253.30   $253.30   $253.30  
  Purchase #2 $13.86   3.686%   $14.3709   $14.37   $14.35   $14.40  
  Purchase #3 $244.73   4.669%   $256.1564   $256.16   $256.15   $256.20  
  Purchase #4 $170.43   8.761%   $185.3614   $185.36   $185.35   $185.40  
  Purchase #5 $60.89   13.664%   $69.21   $69.21   $69.20   $69.20  
  Purchase #6 $198.81   11.673%   $222.0171   $222.02   $222.00   $222.00  
  Purchase #7 $247.34   3.637%   $256.3358   $256.34   $256.35   $256.30  
  7 purchase totals = $1,162.92       $1,256.7521   $1,256.76   $1,256.70   $1,256.80