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	$53.94	3.646%	$55.9067	$55.91	$55.90	$55.90
Purchase #2	$133.51	8.761%	$145.2068	$145.21	$145.20	$145.20
Purchase #3	$31.65	13.492%	$35.9202	$35.92	$35.90	$35.90
Purchase #4	$118.39	3.426%	$122.446	$122.45	$122.45	$122.40
Purchase #5	$71.55	4.169%	$74.5329	$74.53	$74.55	$74.50
Purchase #6	$56.64	8.747%	$61.5943	$61.59	$61.60	$61.60
Purchase #7	$119.58	6.446%	$127.2881	$127.29	$127.30	$127.30
7 purchase totals =	$585.26		$622.8950	$622.90	$622.90	$622.80