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	$48.30	13.125%	$54.6394	$54.64	$54.65	$54.60
Purchase #2	$238.76	10.246%	$263.2233	$263.22	$263.20	$263.20
Purchase #3	$250.56	6.409%	$266.6184	$266.62	$266.60	$266.60
Purchase #4	$92.89	9.670%	$101.8725	$101.87	$101.85	$101.90
Purchase #5	$79.97	11.521%	$89.1833	$89.18	$89.20	$89.20
Purchase #6	$116.73	13.553%	$132.5504	$132.55	$132.55	$132.60
Purchase #7	$40.27	12.709%	$45.3879	$45.39	$45.40	$45.40
7 purchase totals =	$867.48		$953.4752	$953.47	$953.45	$953.50