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	$54.94	3.550%	$56.8904	$56.89	$56.90	$56.90
Purchase #2	$158.98	13.189%	$179.9479	$179.95	$179.95	$179.90
Purchase #3	$214.80	12.825%	$242.3481	$242.35	$242.35	$242.30
Purchase #4	$62.59	12.462%	$70.39	$70.39	$70.40	$70.40
Purchase #5	$176.87	9.413%	$193.5188	$193.52	$193.50	$193.50
Purchase #6	$152.30	8.363%	$165.0368	$165.04	$165.05	$165.00
Purchase #7	$250.92	9.725%	$275.322	$275.32	$275.30	$275.30
7 purchase totals =	$1,071.40		$1,183.4540	$1,183.46	$1,183.45	$1,183.30