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 $110.35   13.735%   $125.5066   $125.51   $125.50   $125.50  
  Purchase #2 $216.88   8.165%   $234.5883   $234.59   $234.60   $234.60  
  Purchase #3 $17.97   10.760%   $19.9036   $19.90   $19.90   $19.90  
  Purchase #4 $250.95   12.317%   $281.8595   $281.86   $281.85   $281.90  
  Purchase #5 $100.32   7.292%   $107.6353   $107.64   $107.65   $107.60  
  Purchase #6 $61.83   13.700%   $70.3007   $70.30   $70.30   $70.30  
  Purchase #7 $68.85   10.130%   $75.8245   $75.82   $75.80   $75.80  
  7 purchase totals = $827.15       $915.6185   $915.62   $915.60   $915.60