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	$149.58	3.157%	$154.3022	$154.30	$154.30	$154.30
Purchase #2	$237.97	7.321%	$255.3918	$255.39	$255.40	$255.40
Purchase #3	$111.83	3.139%	$115.3403	$115.34	$115.35	$115.30
Purchase #4	$90.64	5.574%	$95.6923	$95.69	$95.70	$95.70
Purchase #5	$212.46	8.384%	$230.2726	$230.27	$230.25	$230.30
Purchase #6	$54.52	6.671%	$58.157	$58.16	$58.15	$58.20
Purchase #7	$228.86	6.317%	$243.3171	$243.32	$243.30	$243.30
7 purchase totals =	$1,085.86		$1,152.4733	$1,152.47	$1,152.45	$1,152.50