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	$46.95	11.145%	$52.1826	$52.18	$52.20	$52.20
Purchase #2	$143.69	8.229%	$155.5143	$155.51	$155.50	$155.50
Purchase #3	$11.57	12.234%	$12.9855	$12.99	$13.00	$13.00
Purchase #4	$91.46	10.307%	$100.8868	$100.89	$100.90	$100.90
Purchase #5	$89.92	9.281%	$98.2655	$98.27	$98.25	$98.30
Purchase #6	$104.89	12.868%	$118.3872	$118.39	$118.40	$118.40
Purchase #7	$122.47	9.539%	$134.1524	$134.15	$134.15	$134.20
7 purchase totals =	$610.95		$672.3743	$672.38	$672.40	$672.50