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	$230.88	13.242%	$261.4531	$261.45	$261.45	$261.50
Purchase #2	$153.39	7.479%	$164.862	$164.86	$164.85	$164.90
Purchase #3	$144.88	6.867%	$154.8289	$154.83	$154.85	$154.80
Purchase #4	$65.90	13.261%	$74.639	$74.64	$74.65	$74.60
Purchase #5	$65.43	10.402%	$72.236	$72.24	$72.25	$72.20
Purchase #6	$179.93	13.833%	$204.8197	$204.82	$204.80	$204.80
Purchase #7	$99.29	6.205%	$105.4509	$105.45	$105.45	$105.50
7 purchase totals =	$939.70		$1,038.2896	$1,038.29	$1,038.30	$1,038.30