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	$44.85	12.233%	$50.3365	$50.34	$50.35	$50.30
Purchase #2	$107.75	3.141%	$111.1344	$111.13	$111.15	$111.10
Purchase #3	$53.78	4.278%	$56.0807	$56.08	$56.10	$56.10
Purchase #4	$134.87	12.148%	$151.254	$151.25	$151.25	$151.30
Purchase #5	$232.77	9.168%	$254.1104	$254.11	$254.10	$254.10
Purchase #6	$77.75	13.789%	$88.4709	$88.47	$88.45	$88.50
Purchase #7	$59.46	9.311%	$64.9963	$65.00	$65.00	$65.00
7 purchase totals =	$711.23		$776.3832	$776.38	$776.40	$776.40