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 $242.95   10.514%   $268.4938   $268.49   $268.50   $268.50  
  Purchase #2 $105.37   7.266%   $113.0262   $113.03   $113.05   $113.00  
  Purchase #3 $180.46   9.121%   $196.9198   $196.92   $196.90   $196.90  
  Purchase #4 $215.40   3.715%   $223.4021   $223.40   $223.40   $223.40  
  Purchase #5 $199.31   7.828%   $214.912   $214.91   $214.90   $214.90  
  Purchase #6 $237.34   13.171%   $268.6001   $268.60   $268.60   $268.60  
  Purchase #7 $232.90   11.694%   $260.1353   $260.14   $260.15   $260.10  
  7 purchase totals = $1,413.73       $1,545.4893   $1,545.49   $1,545.50   $1,545.40