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 $77.39   13.205%   $87.6093   $87.61   $87.60   $87.60  
  Purchase #2 $235.42   11.784%   $263.1619   $263.16   $263.15   $263.20  
  Purchase #3 $126.47   10.206%   $139.3775   $139.38   $139.40   $139.40  
  Purchase #4 $248.28   9.862%   $272.7654   $272.77   $272.75   $272.80  
  Purchase #5 $220.77   8.462%   $239.4516   $239.45   $239.45   $239.50  
  Purchase #6 $103.54   12.191%   $116.1626   $116.16   $116.15   $116.20  
  Purchase #7 $89.36   3.844%   $92.795   $92.80   $92.80   $92.80  
  7 purchase totals = $1,101.23       $1,211.3233   $1,211.33   $1,211.30   $1,211.50