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	$78.50	10.404%	$86.6671	$86.67	$86.65	$86.70
Purchase #2	$131.83	9.161%	$143.9069	$143.91	$143.90	$143.90
Purchase #3	$102.31	8.670%	$111.1803	$111.18	$111.20	$111.20
Purchase #4	$122.82	12.114%	$137.6984	$137.70	$137.70	$137.70
Purchase #5	$122.47	3.842%	$127.1753	$127.18	$127.20	$127.20
Purchase #6	$85.97	7.178%	$92.1409	$92.14	$92.15	$92.10
Purchase #7	$187.29	6.192%	$198.887	$198.89	$198.90	$198.90
7 purchase totals =	$831.19		$897.6559	$897.67	$897.70	$897.70