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 $215.63   8.432%   $233.8119   $233.81   $233.80   $233.80  
  Purchase #2 $207.90   3.593%   $215.3698   $215.37   $215.35   $215.40  
  Purchase #3 $46.57   5.698%   $49.2236   $49.22   $49.20   $49.20  
  Purchase #4 $67.61   8.721%   $73.5063   $73.51   $73.50   $73.50  
  Purchase #5 $101.71   12.775%   $114.7035   $114.70   $114.70   $114.70  
  Purchase #6 $107.31   12.860%   $121.1101   $121.11   $121.10   $121.10  
  Purchase #7 $184.25   3.837%   $191.3197   $191.32   $191.30   $191.30  
  7 purchase totals = $930.98       $999.0449   $999.04   $998.95   $999.00