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	$205.42	8.501%	$222.8828	$222.88	$222.90	$222.90
Purchase #2	$67.96	6.295%	$72.2381	$72.24	$72.25	$72.20
Purchase #3	$18.97	9.493%	$20.7708	$20.77	$20.75	$20.80
Purchase #4	$58.85	13.671%	$66.8954	$66.90	$66.90	$66.90
Purchase #5	$237.83	7.507%	$255.6839	$255.68	$255.70	$255.70
Purchase #6	$99.84	12.533%	$112.3529	$112.35	$112.35	$112.40
Purchase #7	$87.63	4.512%	$91.5839	$91.58	$91.60	$91.60
7 purchase totals =	$776.50		$842.4078	$842.40	$842.45	$842.50