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 $59.96   13.754%   $68.2069   $68.21   $68.20   $68.20  
  Purchase #2 $215.39   5.505%   $227.2472   $227.25   $227.25   $227.20  
  Purchase #3 $180.99   10.225%   $199.4962   $199.50   $199.50   $199.50  
  Purchase #4 $77.60   6.609%   $82.7286   $82.73   $82.75   $82.70  
  Purchase #5 $24.94   13.395%   $28.2807   $28.28   $28.30   $28.30  
  Purchase #6 $48.66   8.651%   $52.8696   $52.87   $52.85   $52.90  
  Purchase #7 $181.76   5.553%   $191.8531   $191.85   $191.85   $191.90  
  7 purchase totals = $789.30       $850.6823   $850.69   $850.70   $850.70