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 $184.89   13.452%   $209.7614   $209.76   $209.75   $209.80  
  Purchase #2 $132.88   8.368%   $143.9994   $144.00   $144.00   $144.00  
  Purchase #3 $209.46   7.680%   $225.5465   $225.55   $225.55   $225.50  
  Purchase #4 $49.91   8.757%   $54.2806   $54.28   $54.30   $54.30  
  Purchase #5 $104.50   3.479%   $108.1356   $108.14   $108.15   $108.10  
  Purchase #6 $60.25   6.653%   $64.2584   $64.26   $64.25   $64.30  
  Purchase #7 $192.63   8.449%   $208.9053   $208.91   $208.90   $208.90  
  7 purchase totals = $934.52       $1,014.8872   $1,014.90   $1,014.90   $1,014.90