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 $40.97   9.256%   $44.7622   $44.76   $44.75   $44.80  
  Purchase #2 $100.72   5.125%   $105.8819   $105.88   $105.90   $105.90  
  Purchase #3 $23.69   10.179%   $26.1014   $26.10   $26.10   $26.10  
  Purchase #4 $114.30   13.703%   $129.9625   $129.96   $129.95   $130.00  
  Purchase #5 $144.41   13.677%   $164.161   $164.16   $164.15   $164.20  
  Purchase #6 $204.40   11.106%   $227.1007   $227.10   $227.10   $227.10  
  Purchase #7 $91.30   4.504%   $95.4122   $95.41   $95.40   $95.40  
  7 purchase totals = $719.79       $793.3819   $793.37   $793.35   $793.50