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 $87.96   12.767%   $99.1899   $99.19   $99.20   $99.20  
  Purchase #2 $250.31   5.724%   $264.6377   $264.64   $264.65   $264.60  
  Purchase #3 $51.42   11.597%   $57.3832   $57.38   $57.40   $57.40  
  Purchase #4 $249.53   4.618%   $261.0533   $261.05   $261.05   $261.10  
  Purchase #5 $164.41   4.371%   $171.5964   $171.60   $171.60   $171.60  
  Purchase #6 $46.79   11.485%   $52.1638   $52.16   $52.15   $52.20  
  Purchase #7 $53.48   8.519%   $58.036   $58.04   $58.05   $58.00  
  7 purchase totals = $903.90       $964.0603   $964.06   $964.10   $964.10