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	$169.67	8.183%	$183.5541	$183.55	$183.55	$183.60
Purchase #2	$144.78	9.406%	$158.398	$158.40	$158.40	$158.40
Purchase #3	$38.77	10.208%	$42.7276	$42.73	$42.75	$42.70
Purchase #4	$86.44	5.647%	$91.3213	$91.32	$91.30	$91.30
Purchase #5	$147.51	10.112%	$162.4262	$162.43	$162.45	$162.40
Purchase #6	$50.91	4.587%	$53.2452	$53.25	$53.25	$53.20
Purchase #7	$24.37	13.428%	$27.6424	$27.64	$27.65	$27.60
7 purchase totals =	$662.45		$719.3148	$719.32	$719.35	$719.20