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	$237.32	5.390%	$250.1115	$250.11	$250.10	$250.10
Purchase #2	$131.54	11.564%	$146.7513	$146.75	$146.75	$146.80
Purchase #3	$11.25	12.118%	$12.6133	$12.61	$12.60	$12.60
Purchase #4	$11.59	10.732%	$12.8338	$12.83	$12.85	$12.80
Purchase #5	$11.77	6.826%	$12.5734	$12.57	$12.55	$12.60
Purchase #6	$47.75	5.148%	$50.2082	$50.21	$50.20	$50.20
Purchase #7	$144.36	9.735%	$158.4134	$158.41	$158.40	$158.40
7 purchase totals =	$595.58		$643.5049	$643.49	$643.45	$643.50