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	$165.54	8.218%	$179.1441	$179.14	$179.15	$179.10
Purchase #2	$175.68	11.587%	$196.036	$196.04	$196.05	$196.00
Purchase #3	$53.45	7.861%	$57.6517	$57.65	$57.65	$57.70
Purchase #4	$30.47	13.168%	$34.4823	$34.48	$34.50	$34.50
Purchase #5	$10.86	4.448%	$11.3431	$11.34	$11.35	$11.30
Purchase #6	$171.33	4.627%	$179.2574	$179.26	$179.25	$179.30
Purchase #7	$21.61	4.139%	$22.5044	$22.50	$22.50	$22.50
7 purchase totals =	$628.94		$680.4190	$680.41	$680.45	$680.40