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 $184.49   8.818%   $200.7583   $200.76   $200.75   $200.80  
  Purchase #2 $107.63   12.291%   $120.8588   $120.86   $120.85   $120.90  
  Purchase #3 $176.71   3.404%   $182.7252   $182.73   $182.75   $182.70  
  Purchase #4 $94.61   8.140%   $102.3113   $102.31   $102.30   $102.30  
  Purchase #5 $249.78   4.616%   $261.3098   $261.31   $261.30   $261.30  
  Purchase #6 $114.76   12.256%   $128.825   $128.83   $128.85   $128.80  
  Purchase #7 $107.77   8.592%   $117.0296   $117.03   $117.05   $117.00  
  7 purchase totals = $1,035.75       $1,113.8180   $1,113.83   $1,113.85   $1,113.80