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 $124.62   7.756%   $134.2855   $134.29   $134.30   $134.30  
  Purchase #2 $106.76   7.652%   $114.9293   $114.93   $114.95   $114.90  
  Purchase #3 $115.34   4.563%   $120.603   $120.60   $120.60   $120.60  
  Purchase #4 $173.85   7.696%   $187.2295   $187.23   $187.25   $187.20  
  Purchase #5 $117.42   8.432%   $127.3209   $127.32   $127.30   $127.30  
  Purchase #6 $56.29   8.289%   $60.9559   $60.96   $60.95   $61.00  
  Purchase #7 $27.34   5.749%   $28.9118   $28.91   $28.90   $28.90  
  7 purchase totals = $721.62       $774.2359   $774.24   $774.25   $774.20