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	$17.61	5.755%	$18.6235	$18.62	$18.60	$18.60
Purchase #2	$100.80	11.261%	$112.1511	$112.15	$112.15	$112.20
Purchase #3	$75.29	13.631%	$85.5528	$85.55	$85.55	$85.60
Purchase #4	$166.93	3.495%	$172.7642	$172.76	$172.75	$172.80
Purchase #5	$147.43	13.111%	$166.7595	$166.76	$166.75	$166.80
Purchase #6	$20.78	4.542%	$21.7238	$21.72	$21.70	$21.70
Purchase #7	$29.91	3.669%	$31.0074	$31.01	$31.00	$31.00
7 purchase totals =	$558.75		$608.5823	$608.57	$608.50	$608.70