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	$202.47	13.213%	$229.2224	$229.22	$229.20	$229.20
Purchase #2	$92.60	9.239%	$101.1553	$101.16	$101.15	$101.20
Purchase #3	$72.89	12.611%	$82.0822	$82.08	$82.10	$82.10
Purchase #4	$19.96	3.594%	$20.6774	$20.68	$20.70	$20.70
Purchase #5	$240.97	5.167%	$253.4209	$253.42	$253.40	$253.40
Purchase #6	$81.66	11.360%	$90.9366	$90.94	$90.95	$90.90
Purchase #7	$113.82	12.235%	$127.7459	$127.75	$127.75	$127.70
7 purchase totals =	$824.37		$905.2407	$905.25	$905.25	$905.20