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	$185.29	12.689%	$208.8014	$208.80	$208.80	$208.80
Purchase #2	$79.71	12.248%	$89.4729	$89.47	$89.45	$89.50
Purchase #3	$99.58	4.824%	$104.3837	$104.38	$104.40	$104.40
Purchase #4	$243.89	13.619%	$277.1054	$277.11	$277.10	$277.10
Purchase #5	$33.78	13.752%	$38.4254	$38.43	$38.45	$38.40
Purchase #6	$233.89	8.125%	$252.8936	$252.89	$252.90	$252.90
Purchase #7	$19.65	10.328%	$21.6795	$21.68	$21.70	$21.70
7 purchase totals =	$895.79		$992.7619	$992.76	$992.80	$992.80