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	$37.64	12.616%	$42.3887	$42.39	$42.40	$42.40
Purchase #2	$160.87	7.465%	$172.8789	$172.88	$172.90	$172.90
Purchase #3	$73.53	11.643%	$82.0911	$82.09	$82.10	$82.10
Purchase #4	$107.56	5.447%	$113.4188	$113.42	$113.40	$113.40
Purchase #5	$139.39	10.474%	$153.9897	$153.99	$154.00	$154.00
Purchase #6	$242.85	3.794%	$252.0637	$252.06	$252.05	$252.10
Purchase #7	$144.39	7.659%	$155.4488	$155.45	$155.45	$155.40
7 purchase totals =	$906.23		$972.2797	$972.28	$972.30	$972.30