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 $191.65   6.827%   $204.7339   $204.73   $204.75   $204.70  
  Purchase #2 $175.35   10.117%   $193.0902   $193.09   $193.10   $193.10  
  Purchase #3 $95.49   4.119%   $99.4232   $99.42   $99.40   $99.40  
  Purchase #4 $50.73   6.580%   $54.068   $54.07   $54.05   $54.10  
  Purchase #5 $35.68   8.285%   $38.6361   $38.64   $38.65   $38.60  
  Purchase #6 $205.71   9.598%   $225.454   $225.45   $225.45   $225.50  
  Purchase #7 $136.67   12.111%   $153.2221   $153.22   $153.20   $153.20  
  7 purchase totals = $891.28       $968.6275   $968.62   $968.60   $968.60