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	$139.95	4.116%	$145.7103	$145.71	$145.70	$145.70
Purchase #2	$104.50	6.356%	$111.142	$111.14	$111.15	$111.10
Purchase #3	$151.59	12.349%	$170.3098	$170.31	$170.30	$170.30
Purchase #4	$124.33	6.520%	$132.4363	$132.44	$132.45	$132.40
Purchase #5	$223.33	8.735%	$242.8379	$242.84	$242.85	$242.80
Purchase #6	$126.56	13.569%	$143.7329	$143.73	$143.75	$143.70
Purchase #7	$87.76	5.719%	$92.779	$92.78	$92.80	$92.80
7 purchase totals =	$958.02		$1,038.9482	$1,038.95	$1,039.00	$1,038.80