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 $68.87   9.585%   $75.4712   $75.47   $75.45   $75.50  
  Purchase #2 $224.33   13.765%   $255.209   $255.21   $255.20   $255.20  
  Purchase #3 $125.42   7.480%   $134.8014   $134.80   $134.80   $134.80  
  Purchase #4 $27.67   3.464%   $28.6285   $28.63   $28.65   $28.60  
  Purchase #5 $201.90   3.318%   $208.599   $208.60   $208.60   $208.60  
  Purchase #6 $181.45   12.752%   $204.5885   $204.59   $204.60   $204.60  
  Purchase #7 $38.57   9.117%   $42.0864   $42.09   $42.10   $42.10  
  7 purchase totals = $868.21       $949.3840   $949.39   $949.40   $949.40