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	$45.86	13.783%	$52.1809	$52.18	$52.20	$52.20
Purchase #2	$153.82	13.616%	$174.7641	$174.76	$174.75	$174.80
Purchase #3	$82.67	7.238%	$88.6537	$88.65	$88.65	$88.70
Purchase #4	$173.68	6.838%	$185.5562	$185.56	$185.55	$185.60
Purchase #5	$129.26	13.602%	$146.8419	$146.84	$146.85	$146.80
Purchase #6	$15.54	13.267%	$17.6017	$17.60	$17.60	$17.60
Purchase #7	$89.52	11.677%	$99.9733	$99.97	$99.95	$100.00
7 purchase totals =	$690.35		$765.5718	$765.56	$765.55	$765.70