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 $67.40   8.839%   $73.3575   $73.36   $73.35   $73.40  
  Purchase #2 $249.37   10.675%   $275.9902   $275.99   $276.00   $276.00  
  Purchase #3 $105.58   10.205%   $116.3544   $116.35   $116.35   $116.40  
  Purchase #4 $226.60   8.861%   $246.679   $246.68   $246.70   $246.70  
  Purchase #5 $121.27   12.657%   $136.6191   $136.62   $136.60   $136.60  
  Purchase #6 $13.29   5.864%   $14.0693   $14.07   $14.05   $14.10  
  Purchase #7 $118.42   10.556%   $130.9204   $130.92   $130.90   $130.90  
  7 purchase totals = $901.93       $993.9899   $993.99   $993.95   $994.10