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 $144.77   6.631%   $154.3697   $154.37   $154.35   $154.40  
  Purchase #2 $248.40   13.383%   $281.6434   $281.64   $281.65   $281.60  
  Purchase #3 $218.56   12.676%   $246.2647   $246.26   $246.25   $246.30  
  Purchase #4 $86.40   10.223%   $95.2327   $95.23   $95.25   $95.20  
  Purchase #5 $191.84   13.327%   $217.4065   $217.41   $217.40   $217.40  
  Purchase #6 $217.77   10.402%   $240.4224   $240.42   $240.40   $240.40  
  Purchase #7 $168.99   13.510%   $191.8205   $191.82   $191.80   $191.80  
  7 purchase totals = $1,276.73       $1,427.1599   $1,427.15   $1,427.10   $1,427.10