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 $53.39   13.431%   $60.5608   $60.56   $60.55   $60.60  
  Purchase #2 $195.87   11.166%   $217.7408   $217.74   $217.75   $217.70  
  Purchase #3 $48.53   4.149%   $50.5435   $50.54   $50.55   $50.50  
  Purchase #4 $96.35   10.182%   $106.1604   $106.16   $106.15   $106.20  
  Purchase #5 $159.83   11.276%   $177.8524   $177.85   $177.85   $177.90  
  Purchase #6 $73.76   5.440%   $77.7725   $77.77   $77.75   $77.80  
  Purchase #7 $212.92   4.393%   $222.2736   $222.27   $222.25   $222.30  
  7 purchase totals = $840.65       $912.9040   $912.89   $912.85   $913.00