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	$25.89	6.456%	$27.5615	$27.56	$27.55	$27.60
Purchase #2	$138.51	5.357%	$145.93	$145.93	$145.95	$145.90
Purchase #3	$52.71	13.167%	$59.6503	$59.65	$59.65	$59.70
Purchase #4	$117.58	8.138%	$127.1487	$127.15	$127.15	$127.10
Purchase #5	$138.99	10.245%	$153.2295	$153.23	$153.25	$153.20
Purchase #6	$42.82	3.331%	$44.2463	$44.25	$44.25	$44.20
Purchase #7	$41.43	11.344%	$46.1298	$46.13	$46.15	$46.10
7 purchase totals =	$557.93		$603.8961	$603.90	$603.95	$603.80