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	$190.46	10.459%	$210.3802	$210.38	$210.40	$210.40
Purchase #2	$229.82	3.400%	$237.6339	$237.63	$237.65	$237.60
Purchase #3	$17.41	4.261%	$18.1518	$18.15	$18.15	$18.20
Purchase #4	$65.59	7.501%	$70.5099	$70.51	$70.50	$70.50
Purchase #5	$160.32	7.325%	$172.0634	$172.06	$172.05	$172.10
Purchase #6	$100.26	5.869%	$106.1443	$106.14	$106.15	$106.10
Purchase #7	$94.29	6.363%	$100.2897	$100.29	$100.30	$100.30
7 purchase totals =	$858.15		$915.1732	$915.16	$915.20	$915.20