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 $92.99   6.428%   $98.9674   $98.97   $98.95   $99.00  
  Purchase #2 $249.92   9.205%   $272.9251   $272.93   $272.95   $272.90  
  Purchase #3 $140.53   7.569%   $151.1667   $151.17   $151.15   $151.20  
  Purchase #4 $123.98   8.621%   $134.6683   $134.67   $134.65   $134.70  
  Purchase #5 $192.86   13.737%   $219.3532   $219.35   $219.35   $219.40  
  Purchase #6 $76.37   3.309%   $78.8971   $78.90   $78.90   $78.90  
  Purchase #7 $73.87   5.158%   $77.6802   $77.68   $77.70   $77.70  
  7 purchase totals = $950.52       $1,033.6580   $1,033.67   $1,033.65   $1,033.80