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 $105.91   6.335%   $112.6194   $112.62   $112.60   $112.60  
  Purchase #2 $149.87   10.160%   $165.0968   $165.10   $165.10   $165.10  
  Purchase #3 $108.66   9.758%   $119.263   $119.26   $119.25   $119.30  
  Purchase #4 $99.46   13.716%   $113.1019   $113.10   $113.10   $113.10  
  Purchase #5 $55.35   10.103%   $60.942   $60.94   $60.95   $60.90  
  Purchase #6 $119.94   3.141%   $123.7073   $123.71   $123.70   $123.70  
  Purchase #7 $44.87   5.321%   $47.2575   $47.26   $47.25   $47.30  
  7 purchase totals = $684.06       $741.9879   $741.99   $741.95   $742.00