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	$177.65	3.745%	$184.303	$184.30	$184.30	$184.30
Purchase #2	$100.91	10.205%	$111.2079	$111.21	$111.20	$111.20
Purchase #3	$32.80	13.631%	$37.271	$37.27	$37.25	$37.30
Purchase #4	$74.34	7.628%	$80.0107	$80.01	$80.00	$80.00
Purchase #5	$225.94	9.405%	$247.1897	$247.19	$247.20	$247.20
Purchase #6	$93.95	6.677%	$100.223	$100.22	$100.20	$100.20
Purchase #7	$48.66	12.584%	$54.7834	$54.78	$54.80	$54.80
7 purchase totals =	$754.25		$814.9887	$814.98	$814.95	$815.00