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 $20.71   6.226%   $21.9994   $22.00   $22.00   $22.00  
  Purchase #2 $135.83   3.400%   $140.4482   $140.45   $140.45   $140.40  
  Purchase #3 $219.55   6.461%   $233.7351   $233.74   $233.75   $233.70  
  Purchase #4 $128.54   5.367%   $135.4387   $135.44   $135.45   $135.40  
  Purchase #5 $83.60   7.430%   $89.8115   $89.81   $89.80   $89.80  
  Purchase #6 $66.73   10.106%   $73.4737   $73.47   $73.45   $73.50  
  Purchase #7 $185.68   7.323%   $199.2773   $199.28   $199.30   $199.30  
  7 purchase totals = $840.64       $894.1839   $894.19   $894.20   $894.10