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	$37.93	10.854%	$42.0469	$42.05	$42.05	$42.00
Purchase #2	$8.75	9.872%	$9.6138	$9.61	$9.60	$9.60
Purchase #3	$104.39	4.507%	$109.0949	$109.09	$109.10	$109.10
Purchase #4	$43.61	3.406%	$45.0954	$45.10	$45.10	$45.10
Purchase #5	$85.33	6.391%	$90.7834	$90.78	$90.80	$90.80
Purchase #6	$199.38	8.519%	$216.3652	$216.37	$216.35	$216.40
Purchase #7	$40.51	12.430%	$45.5454	$45.55	$45.55	$45.50
7 purchase totals =	$519.90		$558.5450	$558.55	$558.55	$558.50