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	$23.72	12.627%	$26.7151	$26.72	$26.70	$26.70
Purchase #2	$53.63	3.234%	$55.3644	$55.36	$55.35	$55.40
Purchase #3	$232.52	10.191%	$256.2161	$256.22	$256.20	$256.20
Purchase #4	$149.72	12.820%	$168.9141	$168.91	$168.90	$168.90
Purchase #5	$137.74	11.748%	$153.9217	$153.92	$153.90	$153.90
Purchase #6	$241.63	13.623%	$274.5473	$274.55	$274.55	$274.50
Purchase #7	$39.93	12.724%	$45.0107	$45.01	$45.00	$45.00
7 purchase totals =	$878.89		$980.6894	$980.69	$980.60	$980.60