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	$104.85	12.749%	$118.2173	$118.22	$118.20	$118.20
Purchase #2	$58.61	5.634%	$61.9121	$61.91	$61.90	$61.90
Purchase #3	$46.37	10.379%	$51.1827	$51.18	$51.20	$51.20
Purchase #4	$153.50	11.462%	$171.0942	$171.09	$171.10	$171.10
Purchase #5	$37.55	6.364%	$39.9397	$39.94	$39.95	$39.90
Purchase #6	$164.41	4.842%	$172.3707	$172.37	$172.35	$172.40
Purchase #7	$168.93	13.775%	$192.2001	$192.20	$192.20	$192.20
7 purchase totals =	$734.22		$806.9168	$806.91	$806.90	$806.90