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	$37.90	6.755%	$40.4601	$40.46	$40.45	$40.50
Purchase #2	$40.27	4.846%	$42.2215	$42.22	$42.20	$42.20
Purchase #3	$111.78	6.618%	$119.1776	$119.18	$119.20	$119.20
Purchase #4	$159.95	8.431%	$173.4354	$173.44	$173.45	$173.40
Purchase #5	$176.59	10.686%	$195.4604	$195.46	$195.45	$195.50
Purchase #6	$51.28	13.223%	$58.0608	$58.06	$58.05	$58.10
Purchase #7	$202.62	12.440%	$227.8259	$227.83	$227.85	$227.80
7 purchase totals =	$780.39		$856.6417	$856.65	$856.65	$856.70