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	$163.93	5.114%	$172.3134	$172.31	$172.30	$172.30
Purchase #2	$69.47	12.302%	$78.0162	$78.02	$78.00	$78.00
Purchase #3	$54.43	9.325%	$59.5056	$59.51	$59.50	$59.50
Purchase #4	$105.49	13.269%	$119.4875	$119.49	$119.50	$119.50
Purchase #5	$37.58	4.357%	$39.2174	$39.22	$39.20	$39.20
Purchase #6	$164.42	13.845%	$187.1839	$187.18	$187.20	$187.20
Purchase #7	$143.32	8.433%	$155.4062	$155.41	$155.40	$155.40
7 purchase totals =	$738.64		$811.1302	$811.14	$811.10	$811.10