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	$208.35	10.788%	$230.8268	$230.83	$230.85	$230.80
Purchase #2	$21.73	13.579%	$24.6807	$24.68	$24.70	$24.70
Purchase #3	$249.88	8.574%	$271.3047	$271.30	$271.30	$271.30
Purchase #4	$86.59	13.671%	$98.4277	$98.43	$98.45	$98.40
Purchase #5	$53.68	10.435%	$59.2815	$59.28	$59.30	$59.30
Purchase #6	$199.52	12.470%	$224.4001	$224.40	$224.40	$224.40
Purchase #7	$11.81	9.173%	$12.8933	$12.89	$12.90	$12.90
7 purchase totals =	$831.56		$921.8148	$921.81	$921.90	$921.80