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	$25.60	5.753%	$27.0728	$27.07	$27.05	$27.10
Purchase #2	$77.82	13.781%	$88.5444	$88.54	$88.55	$88.50
Purchase #3	$223.97	3.701%	$232.2591	$232.26	$232.25	$232.30
Purchase #4	$81.88	10.622%	$90.5773	$90.58	$90.60	$90.60
Purchase #5	$201.83	7.786%	$217.5445	$217.54	$217.55	$217.50
Purchase #6	$112.40	13.278%	$127.3245	$127.32	$127.30	$127.30
Purchase #7	$47.69	3.817%	$49.5103	$49.51	$49.50	$49.50
7 purchase totals =	$771.19		$832.8329	$832.82	$832.80	$832.80