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	$159.58	11.806%	$178.42	$178.42	$178.40	$178.40
Purchase #2	$222.66	4.700%	$233.125	$233.13	$233.15	$233.10
Purchase #3	$103.52	13.635%	$117.635	$117.64	$117.65	$117.60
Purchase #4	$191.82	8.582%	$208.282	$208.28	$208.30	$208.30
Purchase #5	$137.54	6.277%	$146.1734	$146.17	$146.15	$146.20
Purchase #6	$73.25	3.381%	$75.7266	$75.73	$75.75	$75.70
Purchase #7	$40.44	5.853%	$42.807	$42.81	$42.80	$42.80
7 purchase totals =	$928.81		$1,002.1690	$1,002.18	$1,002.20	$1,002.10