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 $240.78   8.756%   $261.8627   $261.86   $261.85   $261.90  
  Purchase #2 $222.61   8.548%   $241.6387   $241.64   $241.65   $241.60  
  Purchase #3 $215.97   13.180%   $244.4348   $244.43   $244.45   $244.40  
  Purchase #4 $247.72   8.378%   $268.474   $268.47   $268.45   $268.50  
  Purchase #5 $74.36   10.507%   $82.173   $82.17   $82.15   $82.20  
  Purchase #6 $146.80   10.192%   $161.7619   $161.76   $161.75   $161.80  
  Purchase #7 $48.75   7.152%   $52.2366   $52.24   $52.25   $52.20  
  7 purchase totals = $1,196.99       $1,312.5817   $1,312.57   $1,312.55   $1,312.60