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 $155.77   8.535%   $169.065   $169.07   $169.05   $169.10  
  Purchase #2 $218.59   8.105%   $236.3067   $236.31   $236.30   $236.30  
  Purchase #3 $221.92   4.249%   $231.3494   $231.35   $231.35   $231.30  
  Purchase #4 $159.41   11.209%   $177.2783   $177.28   $177.30   $177.30  
  Purchase #5 $79.37   12.346%   $89.169   $89.17   $89.15   $89.20  
  Purchase #6 $184.91   11.572%   $206.3078   $206.31   $206.30   $206.30  
  Purchase #7 $55.86   7.323%   $59.9506   $59.95   $59.95   $60.00  
  7 purchase totals = $1,075.83       $1,169.4268   $1,169.44   $1,169.40   $1,169.50