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 $12.56   13.368%   $14.239   $14.24   $14.25   $14.20  
  Purchase #2 $35.37   4.367%   $36.9146   $36.91   $36.90   $36.90  
  Purchase #3 $86.65   10.105%   $95.406   $95.41   $95.40   $95.40  
  Purchase #4 $183.86   3.854%   $190.946   $190.95   $190.95   $190.90  
  Purchase #5 $31.71   13.551%   $36.007   $36.01   $36.00   $36.00  
  Purchase #6 $96.30   10.480%   $106.3922   $106.39   $106.40   $106.40  
  Purchase #7 $234.36   5.433%   $247.0928   $247.09   $247.10   $247.10  
  7 purchase totals = $680.81       $726.9976   $727.00   $727.00   $726.90