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	$243.46	8.648%	$264.5144	$264.51	$264.50	$264.50
Purchase #2	$118.64	7.440%	$127.4668	$127.47	$127.45	$127.50
Purchase #3	$87.63	5.415%	$92.3752	$92.38	$92.40	$92.40
Purchase #4	$29.51	9.541%	$32.3255	$32.33	$32.35	$32.30
Purchase #5	$37.71	3.758%	$39.1271	$39.13	$39.15	$39.10
Purchase #6	$151.71	9.808%	$166.5897	$166.59	$166.60	$166.60
Purchase #7	$45.68	9.575%	$50.0539	$50.05	$50.05	$50.10
7 purchase totals =	$714.34		$772.4526	$772.46	$772.50	$772.50