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 $51.69   8.851%   $56.2651   $56.27   $56.25   $56.30  
  Purchase #2 $236.58   13.754%   $269.1192   $269.12   $269.10   $269.10  
  Purchase #3 $132.37   6.118%   $140.4684   $140.47   $140.45   $140.50  
  Purchase #4 $68.99   9.361%   $75.4482   $75.45   $75.45   $75.40  
  Purchase #5 $164.96   6.585%   $175.8226   $175.82   $175.80   $175.80  
  Purchase #6 $115.80   7.428%   $124.4016   $124.40   $124.40   $124.40  
  Purchase #7 $67.97   3.785%   $70.5427   $70.54   $70.55   $70.50  
  7 purchase totals = $838.36       $912.0678   $912.07   $912.00   $912.00