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	$45.68	9.773%	$50.1443	$50.14	$50.15	$50.10
Purchase #2	$147.73	12.215%	$165.7752	$165.78	$165.80	$165.80
Purchase #3	$19.57	7.233%	$20.9855	$20.99	$21.00	$21.00
Purchase #4	$82.84	9.573%	$90.7703	$90.77	$90.75	$90.80
Purchase #5	$152.30	13.546%	$172.9306	$172.93	$172.95	$172.90
Purchase #6	$77.83	3.522%	$80.5712	$80.57	$80.55	$80.60
Purchase #7	$37.73	11.794%	$42.1799	$42.18	$42.20	$42.20
7 purchase totals =	$563.68		$623.3570	$623.36	$623.40	$623.40