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	$239.43	11.267%	$266.4066	$266.41	$266.40	$266.40
Purchase #2	$242.57	9.174%	$264.8234	$264.82	$264.80	$264.80
Purchase #3	$13.77	4.785%	$14.4289	$14.43	$14.45	$14.40
Purchase #4	$158.89	7.177%	$170.2935	$170.29	$170.30	$170.30
Purchase #5	$190.87	4.843%	$200.1138	$200.11	$200.10	$200.10
Purchase #6	$239.66	13.146%	$271.1657	$271.17	$271.15	$271.20
Purchase #7	$100.42	10.783%	$111.2483	$111.25	$111.25	$111.20
7 purchase totals =	$1,185.61		$1,298.4802	$1,298.48	$1,298.45	$1,298.40