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	$61.71	6.180%	$65.5237	$65.52	$65.50	$65.50
Purchase #2	$137.66	9.550%	$150.8065	$150.81	$150.80	$150.80
Purchase #3	$138.84	10.756%	$153.7736	$153.77	$153.75	$153.80
Purchase #4	$14.31	5.244%	$15.0604	$15.06	$15.05	$15.10
Purchase #5	$77.73	10.332%	$85.7611	$85.76	$85.75	$85.80
Purchase #6	$87.51	13.643%	$99.449	$99.45	$99.45	$99.40
Purchase #7	$234.47	8.460%	$254.3062	$254.31	$254.30	$254.30
7 purchase totals =	$752.23		$824.6805	$824.68	$824.60	$824.70