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 $230.49   6.122%   $244.6006   $244.60   $244.60   $244.60  
  Purchase #2 $139.60   4.764%   $146.2505   $146.25   $146.25   $146.30  
  Purchase #3 $59.28   8.318%   $64.2109   $64.21   $64.20   $64.20  
  Purchase #4 $204.27   6.518%   $217.5843   $217.58   $217.60   $217.60  
  Purchase #5 $213.70   10.115%   $235.3158   $235.32   $235.30   $235.30  
  Purchase #6 $73.43   13.344%   $83.2285   $83.23   $83.25   $83.20  
  Purchase #7 $29.28   6.316%   $31.1293   $31.13   $31.15   $31.10  
  7 purchase totals = $950.05       $1,022.3199   $1,022.32   $1,022.35   $1,022.30