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	$89.87	11.406%	$100.1206	$100.12	$100.10	$100.10
Purchase #2	$201.30	10.778%	$222.9961	$223.00	$223.00	$223.00
Purchase #3	$106.97	9.319%	$116.9385	$116.94	$116.95	$116.90
Purchase #4	$130.64	12.231%	$146.6186	$146.62	$146.60	$146.60
Purchase #5	$158.76	10.344%	$175.1821	$175.18	$175.20	$175.20
Purchase #6	$196.93	12.456%	$221.4596	$221.46	$221.45	$221.50
Purchase #7	$149.47	12.157%	$167.6411	$167.64	$167.65	$167.60
7 purchase totals =	$1,033.94		$1,150.9566	$1,150.96	$1,150.95	$1,150.90