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	$132.96	8.624%	$144.4265	$144.43	$144.45	$144.40
Purchase #2	$98.46	5.835%	$104.2051	$104.21	$104.20	$104.20
Purchase #3	$52.80	10.636%	$58.4158	$58.42	$58.40	$58.40
Purchase #4	$161.32	10.371%	$178.0505	$178.05	$178.05	$178.10
Purchase #5	$39.80	13.763%	$45.2777	$45.28	$45.30	$45.30
Purchase #6	$159.37	5.673%	$168.4111	$168.41	$168.40	$168.40
Purchase #7	$189.95	5.657%	$200.6955	$200.70	$200.70	$200.70
7 purchase totals =	$834.66		$899.4822	$899.50	$899.50	$899.50