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	$88.97	13.285%	$100.7897	$100.79	$100.80	$100.80
Purchase #2	$112.52	4.707%	$117.8163	$117.82	$117.80	$117.80
Purchase #3	$207.74	3.636%	$215.2934	$215.29	$215.30	$215.30
Purchase #4	$192.69	12.210%	$216.2174	$216.22	$216.20	$216.20
Purchase #5	$82.42	5.355%	$86.8336	$86.83	$86.85	$86.80
Purchase #6	$158.49	8.805%	$172.445	$172.45	$172.45	$172.40
Purchase #7	$19.33	9.309%	$21.1294	$21.13	$21.15	$21.10
7 purchase totals =	$862.16		$930.5248	$930.53	$930.55	$930.40