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	$72.57	11.340%	$80.7994	$80.80	$80.80	$80.80
Purchase #2	$55.87	3.365%	$57.75	$57.75	$57.75	$57.80
Purchase #3	$83.40	4.111%	$86.8286	$86.83	$86.85	$86.80
Purchase #4	$41.87	6.506%	$44.5941	$44.59	$44.60	$44.60
Purchase #5	$9.77	7.209%	$10.4743	$10.47	$10.45	$10.50
Purchase #6	$150.42	4.834%	$157.6913	$157.69	$157.70	$157.70
Purchase #7	$43.58	4.766%	$45.657	$45.66	$45.65	$45.70
7 purchase totals =	$457.48		$483.7947	$483.79	$483.80	$483.90