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 $84.99   11.694%   $94.9287   $94.93   $94.95   $94.90  
  Purchase #2 $237.36   12.677%   $267.4501   $267.45   $267.45   $267.50  
  Purchase #3 $54.30   6.557%   $57.8605   $57.86   $57.85   $57.90  
  Purchase #4 $225.43   11.110%   $250.4753   $250.48   $250.50   $250.50  
  Purchase #5 $249.85   3.615%   $258.8821   $258.88   $258.90   $258.90  
  Purchase #6 $78.96   9.302%   $86.3049   $86.30   $86.30   $86.30  
  Purchase #7 $105.30   8.560%   $114.3137   $114.31   $114.30   $114.30  
  7 purchase totals = $1,036.19       $1,130.2153   $1,130.21   $1,130.25   $1,130.30