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 $229.42   13.412%   $260.1898   $260.19   $260.20   $260.20  
  Purchase #2 $126.64   7.612%   $136.2798   $136.28   $136.30   $136.30  
  Purchase #3 $97.76   12.659%   $110.1354   $110.14   $110.15   $110.10  
  Purchase #4 $107.58   8.601%   $116.833   $116.83   $116.85   $116.80  
  Purchase #5 $118.39   11.508%   $132.0143   $132.01   $132.00   $132.00  
  Purchase #6 $183.89   4.207%   $191.6263   $191.63   $191.65   $191.60  
  Purchase #7 $205.40   4.796%   $215.251   $215.25   $215.25   $215.30  
  7 purchase totals = $1,069.08       $1,162.3296   $1,162.33   $1,162.40   $1,162.30