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 $112.98   11.651%   $126.1433   $126.14   $126.15   $126.10  
  Purchase #2 $90.63   3.701%   $93.9842   $93.98   $94.00   $94.00  
  Purchase #3 $106.96   8.612%   $116.1714   $116.17   $116.15   $116.20  
  Purchase #4 $237.75   9.872%   $261.2207   $261.22   $261.20   $261.20  
  Purchase #5 $95.25   11.130%   $105.8513   $105.85   $105.85   $105.90  
  Purchase #6 $180.53   13.708%   $205.2771   $205.28   $205.30   $205.30  
  Purchase #7 $250.31   13.518%   $284.1469   $284.15   $284.15   $284.10  
  7 purchase totals = $1,074.41       $1,192.7949   $1,192.79   $1,192.80   $1,192.80