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	$219.87	9.163%	$240.0167	$240.02	$240.00	$240.00
Purchase #2	$92.83	6.802%	$99.1443	$99.14	$99.15	$99.10
Purchase #3	$233.83	4.526%	$244.4131	$244.41	$244.40	$244.40
Purchase #4	$202.37	5.485%	$213.47	$213.47	$213.45	$213.50
Purchase #5	$89.25	7.129%	$95.6126	$95.61	$95.60	$95.60
Purchase #6	$100.89	3.859%	$104.7833	$104.78	$104.80	$104.80
Purchase #7	$172.52	6.537%	$183.7976	$183.80	$183.80	$183.80
7 purchase totals =	$1,111.56		$1,181.2376	$1,181.23	$1,181.20	$1,181.20