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	$107.40	10.730%	$118.924	$118.92	$118.90	$118.90
Purchase #2	$35.51	9.491%	$38.8803	$38.88	$38.90	$38.90
Purchase #3	$51.48	7.456%	$55.3183	$55.32	$55.30	$55.30
Purchase #4	$91.87	8.128%	$99.3372	$99.34	$99.35	$99.30
Purchase #5	$158.51	9.565%	$173.6715	$173.67	$173.65	$173.70
Purchase #6	$176.59	9.130%	$192.7127	$192.71	$192.70	$192.70
Purchase #7	$127.29	8.222%	$137.7558	$137.76	$137.75	$137.80
7 purchase totals =	$748.65		$816.5998	$816.60	$816.55	$816.60