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	$59.85	11.192%	$66.5484	$66.55	$66.55	$66.50
Purchase #2	$126.71	13.568%	$143.902	$143.90	$143.90	$143.90
Purchase #3	$242.54	6.484%	$258.2663	$258.27	$258.25	$258.30
Purchase #4	$181.96	10.505%	$201.0749	$201.07	$201.05	$201.10
Purchase #5	$217.31	9.636%	$238.25	$238.25	$238.25	$238.30
Purchase #6	$211.29	6.784%	$225.6239	$225.62	$225.60	$225.60
Purchase #7	$136.43	7.863%	$147.1575	$147.16	$147.15	$147.20
7 purchase totals =	$1,176.09		$1,280.8230	$1,280.82	$1,280.75	$1,280.90