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 $60.55   4.860%   $63.4927   $63.49   $63.50   $63.50  
  Purchase #2 $242.34   8.468%   $262.8614   $262.86   $262.85   $262.90  
  Purchase #3 $145.29   6.273%   $154.404   $154.40   $154.40   $154.40  
  Purchase #4 $71.54   10.771%   $79.2456   $79.25   $79.25   $79.20  
  Purchase #5 $188.53   9.749%   $206.9098   $206.91   $206.90   $206.90  
  Purchase #6 $236.95   6.719%   $252.8707   $252.87   $252.85   $252.90  
  Purchase #7 $62.26   3.232%   $64.2722   $64.27   $64.25   $64.30  
  7 purchase totals = $1,007.46       $1,084.0564   $1,084.05   $1,084.00   $1,084.10