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 $240.75   9.588%   $263.8331   $263.83   $263.85   $263.80  
  Purchase #2 $149.63   13.129%   $169.2749   $169.27   $169.25   $169.30  
  Purchase #3 $96.33   5.856%   $101.9711   $101.97   $101.95   $102.00  
  Purchase #4 $127.29   7.235%   $136.4994   $136.50   $136.50   $136.50  
  Purchase #5 $208.42   7.633%   $224.3287   $224.33   $224.35   $224.30  
  Purchase #6 $23.51   13.138%   $26.5987   $26.60   $26.60   $26.60  
  Purchase #7 $88.41   8.708%   $96.1087   $96.11   $96.10   $96.10  
  7 purchase totals = $934.34       $1,018.6146   $1,018.61   $1,018.60   $1,018.60