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 $222.87   10.443%   $246.1443   $246.14   $246.15   $246.10  
  Purchase #2 $235.83   13.763%   $268.2873   $268.29   $268.30   $268.30  
  Purchase #3 $98.71   13.412%   $111.949   $111.95   $111.95   $111.90  
  Purchase #4 $141.81   8.266%   $153.532   $153.53   $153.55   $153.50  
  Purchase #5 $243.78   9.515%   $266.9757   $266.98   $267.00   $267.00  
  Purchase #6 $158.60   6.626%   $169.1088   $169.11   $169.10   $169.10  
  Purchase #7 $83.36   8.550%   $90.4873   $90.49   $90.50   $90.50  
  7 purchase totals = $1,184.96       $1,306.4844   $1,306.49   $1,306.55   $1,306.40