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 $169.97   8.335%   $184.137   $184.14   $184.15   $184.10  
  Purchase #2 $229.89   13.643%   $261.2539   $261.25   $261.25   $261.30  
  Purchase #3 $118.89   8.641%   $129.1633   $129.16   $129.15   $129.20  
  Purchase #4 $222.63   4.114%   $231.789   $231.79   $231.80   $231.80  
  Purchase #5 $96.57   5.543%   $101.9229   $101.92   $101.90   $101.90  
  Purchase #6 $145.38   4.345%   $151.6968   $151.70   $151.70   $151.70  
  Purchase #7 $96.97   10.324%   $106.9812   $106.98   $107.00   $107.00  
  7 purchase totals = $1,080.30       $1,166.9441   $1,166.94   $1,166.95   $1,167.00