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	$194.55	13.742%	$221.2851	$221.29	$221.30	$221.30
Purchase #2	$126.99	11.224%	$141.2434	$141.24	$141.25	$141.20
Purchase #3	$60.50	10.483%	$66.8422	$66.84	$66.85	$66.80
Purchase #4	$101.47	7.851%	$109.4364	$109.44	$109.45	$109.40
Purchase #5	$244.85	13.781%	$278.5928	$278.59	$278.60	$278.60
Purchase #6	$193.92	3.206%	$200.1371	$200.14	$200.15	$200.10
Purchase #7	$54.30	6.276%	$57.7079	$57.71	$57.70	$57.70
7 purchase totals =	$976.58		$1,075.2449	$1,075.25	$1,075.30	$1,075.10