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	$40.65	6.578%	$43.324	$43.32	$43.30	$43.30
Purchase #2	$145.65	5.335%	$153.4204	$153.42	$153.40	$153.40
Purchase #3	$123.29	3.382%	$127.4597	$127.46	$127.45	$127.50
Purchase #4	$81.82	12.625%	$92.1498	$92.15	$92.15	$92.10
Purchase #5	$81.96	10.176%	$90.3002	$90.30	$90.30	$90.30
Purchase #6	$54.41	12.599%	$61.2651	$61.27	$61.25	$61.30
Purchase #7	$57.75	13.118%	$65.3256	$65.33	$65.35	$65.30
7 purchase totals =	$585.53		$633.2448	$633.25	$633.20	$633.20