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 $15.47   3.486%   $16.0093   $16.01   $16.00   $16.00  
  Purchase #2 $209.89   9.239%   $229.2817   $229.28   $229.30   $229.30  
  Purchase #3 $215.46   5.251%   $226.7738   $226.77   $226.75   $226.80  
  Purchase #4 $245.89   4.584%   $257.1616   $257.16   $257.15   $257.20  
  Purchase #5 $69.99   11.647%   $78.1417   $78.14   $78.15   $78.10  
  Purchase #6 $189.31   8.802%   $205.9731   $205.97   $205.95   $206.00  
  Purchase #7 $234.63   4.655%   $245.552   $245.55   $245.55   $245.60  
  7 purchase totals = $1,180.64       $1,258.8932   $1,258.88   $1,258.85   $1,259.00