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	$111.63	9.820%	$122.5921	$122.59	$122.60	$122.60
Purchase #2	$171.93	4.411%	$179.5138	$179.51	$179.50	$179.50
Purchase #3	$90.55	10.827%	$100.3538	$100.35	$100.35	$100.40
Purchase #4	$153.79	3.152%	$158.6375	$158.64	$158.65	$158.60
Purchase #5	$24.73	4.803%	$25.9178	$25.92	$25.90	$25.90
Purchase #6	$54.31	4.410%	$56.7051	$56.71	$56.70	$56.70
Purchase #7	$41.51	7.476%	$44.6133	$44.61	$44.60	$44.60
7 purchase totals =	$648.45		$688.3334	$688.33	$688.30	$688.30