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 $118.30   5.216%   $124.4705   $124.47   $124.45   $124.50  
  Purchase #2 $248.64   8.540%   $269.8739   $269.87   $269.85   $269.90  
  Purchase #3 $224.69   7.660%   $241.9013   $241.90   $241.90   $241.90  
  Purchase #4 $231.44   7.720%   $249.3072   $249.31   $249.30   $249.30  
  Purchase #5 $195.71   9.767%   $214.825   $214.83   $214.85   $214.80  
  Purchase #6 $186.28   6.649%   $198.6658   $198.67   $198.65   $198.70  
  Purchase #7 $148.95   5.767%   $157.5399   $157.54   $157.55   $157.50  
  7 purchase totals = $1,354.01       $1,456.5836   $1,456.59   $1,456.55   $1,456.60