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 $208.27   13.599%   $236.5926   $236.59   $236.60   $236.60  
  Purchase #2 $147.90   10.223%   $163.0198   $163.02   $163.00   $163.00  
  Purchase #3 $18.58   13.554%   $21.0983   $21.10   $21.10   $21.10  
  Purchase #4 $117.98   6.440%   $125.5779   $125.58   $125.60   $125.60  
  Purchase #5 $84.85   6.240%   $90.1446   $90.14   $90.15   $90.10  
  Purchase #6 $250.47   10.762%   $277.4256   $277.43   $277.45   $277.40  
  Purchase #7 $152.73   13.532%   $173.3974   $173.40   $173.40   $173.40  
  7 purchase totals = $980.78       $1,087.2562   $1,087.26   $1,087.30   $1,087.20