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	$51.27	6.533%	$54.6195	$54.62	$54.60	$54.60
Purchase #2	$188.35	6.320%	$200.2537	$200.25	$200.25	$200.30
Purchase #3	$146.88	3.676%	$152.2793	$152.28	$152.30	$152.30
Purchase #4	$60.52	9.793%	$66.4467	$66.45	$66.45	$66.40
Purchase #5	$49.90	9.783%	$54.7817	$54.78	$54.80	$54.80
Purchase #6	$142.74	13.376%	$161.8329	$161.83	$161.85	$161.80
Purchase #7	$20.54	7.873%	$22.1571	$22.16	$22.15	$22.20
7 purchase totals =	$660.20		$712.3709	$712.37	$712.40	$712.40