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	$18.26	3.672%	$18.9305	$18.93	$18.95	$18.90
Purchase #2	$231.49	13.563%	$262.887	$262.89	$262.90	$262.90
Purchase #3	$32.71	4.371%	$34.1398	$34.14	$34.15	$34.10
Purchase #4	$162.74	13.667%	$184.9817	$184.98	$185.00	$185.00
Purchase #5	$133.32	9.403%	$145.8561	$145.86	$145.85	$145.90
Purchase #6	$83.66	6.643%	$89.2175	$89.22	$89.20	$89.20
Purchase #7	$57.49	9.224%	$62.7929	$62.79	$62.80	$62.80
7 purchase totals =	$719.67		$798.8055	$798.81	$798.85	$798.80