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	$49.99	9.152%	$54.5651	$54.57	$54.55	$54.60
Purchase #2	$148.37	11.471%	$165.3895	$165.39	$165.40	$165.40
Purchase #3	$155.29	6.853%	$165.932	$165.93	$165.95	$165.90
Purchase #4	$92.69	3.429%	$95.8683	$95.87	$95.85	$95.90
Purchase #5	$176.78	7.777%	$190.5282	$190.53	$190.55	$190.50
Purchase #6	$78.55	8.858%	$85.508	$85.51	$85.50	$85.50
Purchase #7	$120.68	8.157%	$130.5239	$130.52	$130.50	$130.50
7 purchase totals =	$822.35		$888.3150	$888.32	$888.30	$888.30