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 $9.39   7.455%   $10.09   $10.09   $10.10   $10.10  
  Purchase #2 $199.43   5.352%   $210.1035   $210.10   $210.10   $210.10  
  Purchase #3 $240.77   3.563%   $249.3486   $249.35   $249.35   $249.30  
  Purchase #4 $230.63   5.288%   $242.8257   $242.83   $242.85   $242.80  
  Purchase #5 $164.79   4.468%   $172.1528   $172.15   $172.15   $172.20  
  Purchase #6 $136.38   10.569%   $150.794   $150.79   $150.80   $150.80  
  Purchase #7 $6.31   6.160%   $6.6987   $6.70   $6.70   $6.70  
  7 purchase totals = $987.70       $1,042.0133   $1,042.01   $1,042.05   $1,042.00