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 $76.78   12.198%   $86.1456   $86.15   $86.15   $86.10  
  Purchase #2 $84.58   8.656%   $91.9012   $91.90   $91.90   $91.90  
  Purchase #3 $157.84   4.508%   $164.9554   $164.96   $164.95   $165.00  
  Purchase #4 $213.82   10.556%   $236.3908   $236.39   $236.40   $236.40  
  Purchase #5 $12.99   13.612%   $14.7582   $14.76   $14.75   $14.80  
  Purchase #6 $110.41   5.283%   $116.243   $116.24   $116.25   $116.20  
  Purchase #7 $67.73   10.223%   $74.654   $74.65   $74.65   $74.70  
  7 purchase totals = $724.15       $785.0482   $785.05   $785.05   $785.10