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 $22.64   9.739%   $24.8449   $24.84   $24.85   $24.80  
  Purchase #2 $195.69   5.448%   $206.3512   $206.35   $206.35   $206.40  
  Purchase #3 $141.82   3.242%   $146.4178   $146.42   $146.40   $146.40  
  Purchase #4 $246.99   8.555%   $268.12   $268.12   $268.10   $268.10  
  Purchase #5 $159.69   9.394%   $174.6913   $174.69   $174.70   $174.70  
  Purchase #6 $208.57   7.641%   $224.5068   $224.51   $224.50   $224.50  
  Purchase #7 $158.85   3.178%   $163.8983   $163.90   $163.90   $163.90  
  7 purchase totals = $1,134.25       $1,208.8303   $1,208.83   $1,208.80   $1,208.80