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 $248.87   5.779%   $263.2522   $263.25   $263.25   $263.30  
  Purchase #2 $154.96   6.714%   $165.364   $165.36   $165.35   $165.40  
  Purchase #3 $164.35   5.399%   $173.2233   $173.22   $173.20   $173.20  
  Purchase #4 $210.27   13.145%   $237.91   $237.91   $237.90   $237.90  
  Purchase #5 $123.81   9.800%   $135.9434   $135.94   $135.95   $135.90  
  Purchase #6 $163.76   13.530%   $185.9167   $185.92   $185.90   $185.90  
  Purchase #7 $117.86   4.453%   $123.1083   $123.11   $123.10   $123.10  
  7 purchase totals = $1,183.88       $1,284.7179   $1,284.71   $1,284.65   $1,284.70