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 $88.63   6.833%   $94.6861   $94.69   $94.70   $94.70  
  Purchase #2 $60.61   11.819%   $67.7735   $67.77   $67.75   $67.80  
  Purchase #3 $8.74   4.655%   $9.1468   $9.15   $9.15   $9.10  
  Purchase #4 $167.44   6.567%   $178.4358   $178.44   $178.45   $178.40  
  Purchase #5 $239.28   3.771%   $248.3032   $248.30   $248.30   $248.30  
  Purchase #6 $185.87   3.768%   $192.8736   $192.87   $192.85   $192.90  
  Purchase #7 $111.99   6.116%   $118.8393   $118.84   $118.85   $118.80  
  7 purchase totals = $862.56       $910.0583   $910.06   $910.05   $910.00