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	$133.59	6.565%	$142.3602	$142.36	$142.35	$142.40
Purchase #2	$106.68	7.104%	$114.2585	$114.26	$114.25	$114.30
Purchase #3	$77.72	5.741%	$82.1819	$82.18	$82.20	$82.20
Purchase #4	$144.29	4.727%	$151.1106	$151.11	$151.10	$151.10
Purchase #5	$191.36	13.719%	$217.6127	$217.61	$217.60	$217.60
Purchase #6	$81.87	10.466%	$90.4385	$90.44	$90.45	$90.40
Purchase #7	$169.32	12.712%	$190.844	$190.84	$190.85	$190.80
7 purchase totals =	$904.83		$988.8064	$988.80	$988.80	$988.80