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	$172.73	12.265%	$193.9153	$193.92	$193.90	$193.90
Purchase #2	$48.77	13.757%	$55.4793	$55.48	$55.50	$55.50
Purchase #3	$19.83	9.859%	$21.785	$21.79	$21.80	$21.80
Purchase #4	$49.62	7.836%	$53.5082	$53.51	$53.50	$53.50
Purchase #5	$96.92	3.186%	$100.0079	$100.01	$100.00	$100.00
Purchase #6	$208.68	10.270%	$230.1114	$230.11	$230.10	$230.10
Purchase #7	$150.62	11.248%	$167.5617	$167.56	$167.55	$167.60
7 purchase totals =	$747.17		$822.3688	$822.38	$822.35	$822.40