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	$180.61	13.790%	$205.5161	$205.52	$205.50	$205.50
Purchase #2	$98.94	6.263%	$105.1366	$105.14	$105.15	$105.10
Purchase #3	$53.65	11.211%	$59.6647	$59.66	$59.65	$59.70
Purchase #4	$173.40	5.775%	$183.4139	$183.41	$183.40	$183.40
Purchase #5	$129.96	5.760%	$137.4457	$137.45	$137.45	$137.40
Purchase #6	$74.41	10.501%	$82.2238	$82.22	$82.20	$82.20
Purchase #7	$34.47	12.560%	$38.7994	$38.80	$38.80	$38.80
7 purchase totals =	$745.44		$812.2002	$812.20	$812.15	$812.10