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	$88.43	12.253%	$99.2653	$99.27	$99.25	$99.30
Purchase #2	$158.51	9.681%	$173.8554	$173.86	$173.85	$173.90
Purchase #3	$139.33	4.340%	$145.3769	$145.38	$145.40	$145.40
Purchase #4	$97.69	4.365%	$101.9542	$101.95	$101.95	$102.00
Purchase #5	$108.90	4.342%	$113.6284	$113.63	$113.65	$113.60
Purchase #6	$127.72	3.421%	$132.0893	$132.09	$132.10	$132.10
Purchase #7	$5.52	7.665%	$5.9431	$5.94	$5.95	$5.90
7 purchase totals =	$726.10		$772.1126	$772.12	$772.15	$772.20