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	$244.30	10.324%	$269.5215	$269.52	$269.50	$269.50
Purchase #2	$80.78	13.102%	$91.3638	$91.36	$91.35	$91.40
Purchase #3	$184.82	8.238%	$200.0455	$200.05	$200.05	$200.00
Purchase #4	$86.71	13.443%	$98.3664	$98.37	$98.35	$98.40
Purchase #5	$18.41	6.593%	$19.6238	$19.62	$19.60	$19.60
Purchase #6	$10.85	4.479%	$11.336	$11.34	$11.35	$11.30
Purchase #7	$129.50	10.760%	$143.4342	$143.43	$143.45	$143.40
7 purchase totals =	$755.37		$833.6912	$833.69	$833.65	$833.60