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	$81.60	13.125%	$92.31	$92.31	$92.30	$92.30
Purchase #2	$157.77	3.130%	$162.7082	$162.71	$162.70	$162.70
Purchase #3	$133.40	8.411%	$144.6203	$144.62	$144.60	$144.60
Purchase #4	$78.51	8.637%	$85.2909	$85.29	$85.30	$85.30
Purchase #5	$170.31	9.116%	$185.8355	$185.84	$185.85	$185.80
Purchase #6	$13.78	10.461%	$15.2215	$15.22	$15.20	$15.20
Purchase #7	$172.72	13.172%	$195.4707	$195.47	$195.45	$195.50
7 purchase totals =	$808.09		$881.4571	$881.46	$881.40	$881.40