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	$135.39	13.126%	$153.1613	$153.16	$153.15	$153.20
Purchase #2	$141.67	8.123%	$153.1779	$153.18	$153.20	$153.20
Purchase #3	$58.96	5.538%	$62.2252	$62.23	$62.25	$62.20
Purchase #4	$139.38	8.693%	$151.4963	$151.50	$151.50	$151.50
Purchase #5	$49.55	7.617%	$53.3242	$53.32	$53.30	$53.30
Purchase #6	$44.42	9.230%	$48.52	$48.52	$48.50	$48.50
Purchase #7	$172.84	9.380%	$189.0524	$189.05	$189.05	$189.10
7 purchase totals =	$742.21		$810.9573	$810.96	$810.95	$811.00