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	$18.82	12.841%	$21.2367	$21.24	$21.25	$21.20
Purchase #2	$218.73	6.773%	$233.5446	$233.54	$233.55	$233.50
Purchase #3	$58.73	5.329%	$61.8597	$61.86	$61.85	$61.90
Purchase #4	$87.69	12.694%	$98.8214	$98.82	$98.80	$98.80
Purchase #5	$152.68	7.415%	$164.0012	$164.00	$164.00	$164.00
Purchase #6	$9.77	6.541%	$10.4091	$10.41	$10.40	$10.40
Purchase #7	$181.32	8.215%	$196.2154	$196.22	$196.20	$196.20
7 purchase totals =	$727.74		$786.0881	$786.09	$786.05	$786.00