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	$19.99	3.513%	$20.6922	$20.69	$20.70	$20.70
Purchase #2	$227.43	3.612%	$235.6448	$235.64	$235.65	$235.60
Purchase #3	$99.69	11.680%	$111.3338	$111.33	$111.35	$111.30
Purchase #4	$24.34	6.602%	$25.9469	$25.95	$25.95	$25.90
Purchase #5	$137.36	3.260%	$141.8379	$141.84	$141.85	$141.80
Purchase #6	$153.94	12.113%	$172.5868	$172.59	$172.60	$172.60
Purchase #7	$147.44	7.454%	$158.4302	$158.43	$158.45	$158.40
7 purchase totals =	$810.19		$866.4726	$866.47	$866.55	$866.30