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	$92.97	7.613%	$100.0478	$100.05	$100.05	$100.00
Purchase #2	$182.38	12.825%	$205.7702	$205.77	$205.75	$205.80
Purchase #3	$178.25	5.802%	$188.5921	$188.59	$188.60	$188.60
Purchase #4	$145.96	4.446%	$152.4494	$152.45	$152.45	$152.40
Purchase #5	$52.43	11.607%	$58.5156	$58.52	$58.50	$58.50
Purchase #6	$184.95	11.266%	$205.7865	$205.79	$205.80	$205.80
Purchase #7	$163.68	3.777%	$169.8622	$169.86	$169.85	$169.90
7 purchase totals =	$1,000.62		$1,081.0238	$1,081.03	$1,081.00	$1,081.00