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	$143.64	12.301%	$161.3092	$161.31	$161.30	$161.30
Purchase #2	$40.64	3.392%	$42.0185	$42.02	$42.00	$42.00
Purchase #3	$34.65	8.204%	$37.4927	$37.49	$37.50	$37.50
Purchase #4	$122.79	6.459%	$130.721	$130.72	$130.70	$130.70
Purchase #5	$46.79	11.388%	$52.1184	$52.12	$52.10	$52.10
Purchase #6	$46.65	4.640%	$48.8146	$48.81	$48.80	$48.80
Purchase #7	$189.73	5.459%	$200.0874	$200.09	$200.10	$200.10
7 purchase totals =	$624.89		$672.5618	$672.56	$672.50	$672.50