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 $33.63   3.824%   $34.916   $34.92   $34.90   $34.90  
  Purchase #2 $48.88   8.176%   $52.8764   $52.88   $52.90   $52.90  
  Purchase #3 $17.63   9.313%   $19.2719   $19.27   $19.25   $19.30  
  Purchase #4 $74.49   8.275%   $80.654   $80.65   $80.65   $80.70  
  Purchase #5 $214.54   8.794%   $233.4066   $233.41   $233.40   $233.40  
  Purchase #6 $244.85   13.175%   $277.109   $277.11   $277.10   $277.10  
  Purchase #7 $233.90   10.390%   $258.2022   $258.20   $258.20   $258.20  
  7 purchase totals = $867.92       $956.4361   $956.44   $956.40   $956.50