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 $61.40   3.675%   $63.6565   $63.66   $63.65   $63.70  
  Purchase #2 $88.71   8.501%   $96.2512   $96.25   $96.25   $96.30  
  Purchase #3 $207.69   3.405%   $214.7618   $214.76   $214.75   $214.80  
  Purchase #4 $131.46   13.449%   $149.1401   $149.14   $149.15   $149.10  
  Purchase #5 $110.45   3.340%   $114.139   $114.14   $114.15   $114.10  
  Purchase #6 $13.35   8.213%   $14.4464   $14.45   $14.45   $14.40  
  Purchase #7 $114.48   12.802%   $129.1357   $129.14   $129.15   $129.10  
  7 purchase totals = $727.54       $781.5307   $781.54   $781.55   $781.50