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 $54.42   6.434%   $57.9214   $57.92   $57.90   $57.90  
  Purchase #2 $65.68   4.726%   $68.784   $68.78   $68.80   $68.80  
  Purchase #3 $114.97   3.237%   $118.6916   $118.69   $118.70   $118.70  
  Purchase #4 $192.39   12.215%   $215.8904   $215.89   $215.90   $215.90  
  Purchase #5 $93.40   8.509%   $101.3474   $101.35   $101.35   $101.30  
  Purchase #6 $201.30   11.674%   $224.7998   $224.80   $224.80   $224.80  
  Purchase #7 $248.59   5.342%   $261.8697   $261.87   $261.85   $261.90  
  7 purchase totals = $970.75       $1,049.3043   $1,049.30   $1,049.30   $1,049.30