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 $203.48   11.388%   $226.6523   $226.65   $226.65   $226.70  
  Purchase #2 $70.47   6.497%   $75.0484   $75.05   $75.05   $75.00  
  Purchase #3 $158.38   6.559%   $168.7681   $168.77   $168.75   $168.80  
  Purchase #4 $160.25   6.541%   $170.732   $170.73   $170.75   $170.70  
  Purchase #5 $244.58   4.871%   $256.4935   $256.49   $256.50   $256.50  
  Purchase #6 $11.45   7.601%   $12.3203   $12.32   $12.30   $12.30  
  Purchase #7 $109.47   5.297%   $115.2686   $115.27   $115.25   $115.30  
  7 purchase totals = $958.08       $1,025.2832   $1,025.28   $1,025.25   $1,025.30