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 $61.31   11.851%   $68.5758   $68.58   $68.60   $68.60  
  Purchase #2 $108.27   10.203%   $119.3168   $119.32   $119.30   $119.30  
  Purchase #3 $207.88   9.623%   $227.8843   $227.88   $227.90   $227.90  
  Purchase #4 $130.31   5.457%   $137.421   $137.42   $137.40   $137.40  
  Purchase #5 $86.75   5.183%   $91.2463   $91.25   $91.25   $91.20  
  Purchase #6 $37.76   6.303%   $40.14   $40.14   $40.15   $40.10  
  Purchase #7 $109.88   8.874%   $119.6308   $119.63   $119.65   $119.60  
  7 purchase totals = $742.16       $804.2150   $804.22   $804.25   $804.10