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 $76.91   9.570%   $84.2703   $84.27   $84.25   $84.30  
  Purchase #2 $211.53   3.484%   $218.8997   $218.90   $218.90   $218.90  
  Purchase #3 $224.36   9.172%   $244.9383   $244.94   $244.95   $244.90  
  Purchase #4 $144.61   12.598%   $162.828   $162.83   $162.85   $162.80  
  Purchase #5 $143.95   9.444%   $157.5446   $157.54   $157.55   $157.50  
  Purchase #6 $21.90   4.703%   $22.93   $22.93   $22.95   $22.90  
  Purchase #7 $250.97   4.628%   $262.5849   $262.58   $262.60   $262.60  
  7 purchase totals = $1,074.23       $1,153.9958   $1,153.99   $1,154.05   $1,153.90