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 $88.96   10.340%   $98.1585   $98.16   $98.15   $98.20  
  Purchase #2 $157.66   7.149%   $168.9311   $168.93   $168.95   $168.90  
  Purchase #3 $120.45   4.780%   $126.2075   $126.21   $126.20   $126.20  
  Purchase #4 $209.26   13.230%   $236.9451   $236.95   $236.95   $236.90  
  Purchase #5 $200.75   8.273%   $217.358   $217.36   $217.35   $217.40  
  Purchase #6 $248.47   9.215%   $271.3665   $271.37   $271.35   $271.40  
  Purchase #7 $63.77   7.190%   $68.3551   $68.36   $68.35   $68.40  
  7 purchase totals = $1,089.32       $1,187.3218   $1,187.34   $1,187.30   $1,187.40