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	$109.74	10.807%	$121.5996	$121.60	$121.60	$121.60
Purchase #2	$100.51	3.742%	$104.2711	$104.27	$104.25	$104.30
Purchase #3	$88.27	13.704%	$100.3665	$100.37	$100.35	$100.40
Purchase #4	$97.40	11.308%	$108.414	$108.41	$108.40	$108.40
Purchase #5	$112.97	13.547%	$128.274	$128.27	$128.25	$128.30
Purchase #6	$235.75	11.778%	$263.5166	$263.52	$263.50	$263.50
Purchase #7	$193.87	9.252%	$211.8069	$211.81	$211.80	$211.80
7 purchase totals =	$938.51		$1,038.2487	$1,038.25	$1,038.15	$1,038.30