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 $237.51   4.631%   $248.5091   $248.51   $248.50   $248.50  
  Purchase #2 $146.57   3.668%   $151.9462   $151.95   $151.95   $151.90  
  Purchase #3 $68.75   5.574%   $72.5821   $72.58   $72.60   $72.60  
  Purchase #4 $73.78   5.608%   $77.9176   $77.92   $77.90   $77.90  
  Purchase #5 $178.63   8.668%   $194.1136   $194.11   $194.10   $194.10  
  Purchase #6 $226.34   12.437%   $254.4899   $254.49   $254.50   $254.50  
  Purchase #7 $232.55   7.501%   $249.9936   $249.99   $250.00   $250.00  
  7 purchase totals = $1,164.13       $1,249.5521   $1,249.55   $1,249.55   $1,249.50