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	$49.69	11.378%	$55.3437	$55.34	$55.35	$55.30
Purchase #2	$43.55	11.335%	$48.4864	$48.49	$48.50	$48.50
Purchase #3	$99.29	4.234%	$103.4939	$103.49	$103.50	$103.50
Purchase #4	$49.95	6.680%	$53.2867	$53.29	$53.30	$53.30
Purchase #5	$109.35	10.233%	$120.5398	$120.54	$120.55	$120.50
Purchase #6	$183.36	10.653%	$202.8933	$202.89	$202.90	$202.90
Purchase #7	$144.59	9.395%	$158.1742	$158.17	$158.15	$158.20
7 purchase totals =	$679.78		$742.2180	$742.21	$742.25	$742.20