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	$172.66	8.388%	$187.1427	$187.14	$187.15	$187.10
Purchase #2	$165.76	12.186%	$185.9595	$185.96	$185.95	$186.00
Purchase #3	$82.78	9.689%	$90.8006	$90.80	$90.80	$90.80
Purchase #4	$250.65	13.396%	$284.2271	$284.23	$284.25	$284.20
Purchase #5	$74.92	9.255%	$81.8538	$81.85	$81.85	$81.90
Purchase #6	$239.73	6.836%	$256.1179	$256.12	$256.10	$256.10
Purchase #7	$94.42	4.240%	$98.4234	$98.42	$98.40	$98.40
7 purchase totals =	$1,080.92		$1,184.5250	$1,184.52	$1,184.50	$1,184.50