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	$77.60	3.502%	$80.3176	$80.32	$80.30	$80.30
Purchase #2	$138.56	4.371%	$144.6165	$144.62	$144.60	$144.60
Purchase #3	$180.37	12.108%	$202.2092	$202.21	$202.20	$202.20
Purchase #4	$52.53	13.150%	$59.4377	$59.44	$59.45	$59.40
Purchase #5	$56.55	5.464%	$59.6399	$59.64	$59.65	$59.60
Purchase #6	$14.42	7.680%	$15.5275	$15.53	$15.55	$15.50
Purchase #7	$9.70	4.855%	$10.1709	$10.17	$10.15	$10.20
7 purchase totals =	$529.73		$571.9193	$571.93	$571.90	$571.80