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 $96.98   5.472%   $102.2867   $102.29   $102.30   $102.30  
  Purchase #2 $229.49   8.128%   $248.1429   $248.14   $248.15   $248.10  
  Purchase #3 $142.66   10.659%   $157.8661   $157.87   $157.85   $157.90  
  Purchase #4 $49.85   3.132%   $51.4113   $51.41   $51.40   $51.40  
  Purchase #5 $76.61   3.160%   $79.0309   $79.03   $79.05   $79.00  
  Purchase #6 $244.74   10.709%   $270.9492   $270.95   $270.95   $270.90  
  Purchase #7 $106.58   9.721%   $116.9406   $116.94   $116.95   $116.90  
  7 purchase totals = $946.91       $1,026.6277   $1,026.63   $1,026.65   $1,026.50