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	$6.42	10.450%	$7.0909	$7.09	$7.10	$7.10
Purchase #2	$127.54	12.569%	$143.5705	$143.57	$143.55	$143.60
Purchase #3	$132.62	9.823%	$145.6473	$145.65	$145.65	$145.60
Purchase #4	$135.54	8.114%	$146.5377	$146.54	$146.55	$146.50
Purchase #5	$211.65	10.656%	$234.2034	$234.20	$234.20	$234.20
Purchase #6	$219.38	6.273%	$233.1417	$233.14	$233.15	$233.10
Purchase #7	$162.89	11.422%	$181.4953	$181.50	$181.50	$181.50
7 purchase totals =	$996.04		$1,091.6868	$1,091.69	$1,091.70	$1,091.60