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 $217.75   3.315%   $224.9684   $224.97   $224.95   $225.00  
  Purchase #2 $22.39   10.289%   $24.6937   $24.69   $24.70   $24.70  
  Purchase #3 $85.65   7.717%   $92.2596   $92.26   $92.25   $92.30  
  Purchase #4 $208.26   13.210%   $235.7711   $235.77   $235.75   $235.80  
  Purchase #5 $75.66   5.227%   $79.6147   $79.61   $79.60   $79.60  
  Purchase #6 $121.59   8.603%   $132.0504   $132.05   $132.05   $132.10  
  Purchase #7 $110.77   13.657%   $125.8979   $125.90   $125.90   $125.90  
  7 purchase totals = $842.07       $915.2558   $915.25   $915.20   $915.40