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	$70.77	9.634%	$77.588	$77.59	$77.60	$77.60
Purchase #2	$137.80	10.227%	$151.8928	$151.89	$151.90	$151.90
Purchase #3	$233.90	13.445%	$265.3479	$265.35	$265.35	$265.30
Purchase #4	$182.41	5.447%	$192.3459	$192.35	$192.35	$192.30
Purchase #5	$49.94	13.798%	$56.8307	$56.83	$56.85	$56.80
Purchase #6	$42.95	4.870%	$45.0417	$45.04	$45.05	$45.00
Purchase #7	$173.77	11.624%	$193.969	$193.97	$193.95	$194.00
7 purchase totals =	$891.54		$983.0160	$983.02	$983.05	$982.90