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	$16.80	7.579%	$18.0733	$18.07	$18.05	$18.10
Purchase #2	$111.52	10.819%	$123.5853	$123.59	$123.60	$123.60
Purchase #3	$52.30	9.862%	$57.4578	$57.46	$57.45	$57.50
Purchase #4	$79.88	10.163%	$87.9982	$88.00	$88.00	$88.00
Purchase #5	$179.92	6.552%	$191.7084	$191.71	$191.70	$191.70
Purchase #6	$60.66	3.240%	$62.6254	$62.63	$62.65	$62.60
Purchase #7	$6.74	10.283%	$7.4331	$7.43	$7.45	$7.40
7 purchase totals =	$507.82		$548.8815	$548.89	$548.90	$548.90