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	$51.82	8.493%	$56.2211	$56.22	$56.20	$56.20
Purchase #2	$78.67	4.609%	$82.2959	$82.30	$82.30	$82.30
Purchase #3	$150.97	11.841%	$168.8464	$168.85	$168.85	$168.80
Purchase #4	$195.32	11.838%	$218.442	$218.44	$218.45	$218.40
Purchase #5	$213.52	9.210%	$233.1852	$233.19	$233.20	$233.20
Purchase #6	$163.97	12.685%	$184.7696	$184.77	$184.75	$184.80
Purchase #7	$250.76	7.207%	$268.8323	$268.83	$268.85	$268.80
7 purchase totals =	$1,105.03		$1,212.5925	$1,212.60	$1,212.60	$1,212.50