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 $39.64   4.709%   $41.5066   $41.51   $41.50   $41.50  
  Purchase #2 $190.67   4.175%   $198.6305   $198.63   $198.65   $198.60  
  Purchase #3 $202.56   10.455%   $223.7376   $223.74   $223.75   $223.70  
  Purchase #4 $216.81   10.118%   $238.7468   $238.75   $238.75   $238.70  
  Purchase #5 $154.51   12.150%   $173.283   $173.28   $173.30   $173.30  
  Purchase #6 $196.90   6.855%   $210.3975   $210.40   $210.40   $210.40  
  Purchase #7 $217.99   11.423%   $242.891   $242.89   $242.90   $242.90  
  7 purchase totals = $1,219.08       $1,329.1930   $1,329.20   $1,329.25   $1,329.10