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	$11.42	9.555%	$12.5112	$12.51	$12.50	$12.50
Purchase #2	$238.74	4.839%	$250.2926	$250.29	$250.30	$250.30
Purchase #3	$146.80	10.464%	$162.1612	$162.16	$162.15	$162.20
Purchase #4	$228.46	4.326%	$238.3432	$238.34	$238.35	$238.30
Purchase #5	$71.66	13.680%	$81.4631	$81.46	$81.45	$81.50
Purchase #6	$80.99	8.358%	$87.7591	$87.76	$87.75	$87.80
Purchase #7	$240.48	13.376%	$272.6466	$272.65	$272.65	$272.60
7 purchase totals =	$1,018.55		$1,105.1770	$1,105.17	$1,105.15	$1,105.20