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	$41.68	8.259%	$45.1224	$45.12	$45.10	$45.10
Purchase #2	$121.30	5.137%	$127.5312	$127.53	$127.55	$127.50
Purchase #3	$86.43	6.190%	$91.78	$91.78	$91.80	$91.80
Purchase #4	$159.96	3.786%	$166.0161	$166.02	$166.00	$166.00
Purchase #5	$126.99	4.248%	$132.3845	$132.38	$132.40	$132.40
Purchase #6	$161.66	12.103%	$181.2257	$181.23	$181.25	$181.20
Purchase #7	$77.25	10.506%	$85.3659	$85.37	$85.35	$85.40
7 purchase totals =	$775.27		$829.4258	$829.43	$829.45	$829.40