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	$11.88	13.322%	$13.4627	$13.46	$13.45	$13.50
Purchase #2	$64.93	10.353%	$71.6522	$71.65	$71.65	$71.70
Purchase #3	$24.37	8.752%	$26.5029	$26.50	$26.50	$26.50
Purchase #4	$143.36	4.724%	$150.1323	$150.13	$150.15	$150.10
Purchase #5	$179.41	7.271%	$192.4549	$192.45	$192.45	$192.50
Purchase #6	$6.41	11.665%	$7.1577	$7.16	$7.15	$7.20
Purchase #7	$51.88	9.665%	$56.8942	$56.89	$56.90	$56.90
7 purchase totals =	$482.24		$518.2569	$518.24	$518.25	$518.40