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	$126.37	13.459%	$143.3781	$143.38	$143.40	$143.40
Purchase #2	$80.65	3.287%	$83.301	$83.30	$83.30	$83.30
Purchase #3	$248.36	11.845%	$277.7782	$277.78	$277.80	$277.80
Purchase #4	$191.29	8.809%	$208.1407	$208.14	$208.15	$208.10
Purchase #5	$70.25	11.293%	$78.1833	$78.18	$78.20	$78.20
Purchase #6	$45.74	10.522%	$50.5528	$50.55	$50.55	$50.60
Purchase #7	$151.47	9.121%	$165.2856	$165.29	$165.30	$165.30
7 purchase totals =	$914.13		$1,006.6197	$1,006.62	$1,006.70	$1,006.70