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	$179.82	3.125%	$185.4394	$185.44	$185.45	$185.40
Purchase #2	$105.75	8.685%	$114.9344	$114.93	$114.95	$114.90
Purchase #3	$112.97	12.296%	$126.8608	$126.86	$126.85	$126.90
Purchase #4	$19.48	6.706%	$20.7863	$20.79	$20.80	$20.80
Purchase #5	$172.64	9.138%	$188.4158	$188.42	$188.40	$188.40
Purchase #6	$105.61	5.316%	$111.2242	$111.22	$111.20	$111.20
Purchase #7	$202.75	3.704%	$210.2599	$210.26	$210.25	$210.30
7 purchase totals =	$899.02		$957.9208	$957.92	$957.90	$957.90