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	$7.51	13.820%	$8.5479	$8.55	$8.55	$8.50
Purchase #2	$193.56	7.670%	$208.4061	$208.41	$208.40	$208.40
Purchase #3	$126.41	8.293%	$136.8932	$136.89	$136.90	$136.90
Purchase #4	$201.93	4.283%	$210.5787	$210.58	$210.60	$210.60
Purchase #5	$172.58	7.668%	$185.8134	$185.81	$185.80	$185.80
Purchase #6	$52.78	12.337%	$59.2915	$59.29	$59.30	$59.30
Purchase #7	$30.48	13.574%	$34.6174	$34.62	$34.60	$34.60
7 purchase totals =	$785.25		$844.1482	$844.15	$844.15	$844.10