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	$87.27	4.188%	$90.9249	$90.92	$90.90	$90.90
Purchase #2	$224.72	13.339%	$254.6954	$254.70	$254.70	$254.70
Purchase #3	$241.85	7.180%	$259.2148	$259.21	$259.20	$259.20
Purchase #4	$157.64	11.826%	$176.2825	$176.28	$176.30	$176.30
Purchase #5	$150.72	3.395%	$155.8369	$155.84	$155.85	$155.80
Purchase #6	$183.46	8.400%	$198.8706	$198.87	$198.85	$198.90
Purchase #7	$101.32	10.109%	$111.5624	$111.56	$111.55	$111.60
7 purchase totals =	$1,146.98		$1,247.3875	$1,247.38	$1,247.35	$1,247.40