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 $196.49   6.322%   $208.9121   $208.91   $208.90   $208.90  
  Purchase #2 $231.49   8.695%   $251.6181   $251.62   $251.60   $251.60  
  Purchase #3 $8.41   13.375%   $9.5348   $9.53   $9.55   $9.50  
  Purchase #4 $64.72   4.447%   $67.5981   $67.60   $67.60   $67.60  
  Purchase #5 $208.68   3.228%   $215.4162   $215.42   $215.40   $215.40  
  Purchase #6 $8.68   7.532%   $9.3338   $9.33   $9.35   $9.30  
  Purchase #7 $162.91   5.323%   $171.5817   $171.58   $171.60   $171.60  
  7 purchase totals = $881.38       $933.9948   $933.99   $934.00   $933.90