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	$68.52	4.354%	$71.5034	$71.50	$71.50	$71.50
Purchase #2	$149.90	5.545%	$158.212	$158.21	$158.20	$158.20
Purchase #3	$41.71	7.532%	$44.8516	$44.85	$44.85	$44.90
Purchase #4	$136.76	4.622%	$143.081	$143.08	$143.10	$143.10
Purchase #5	$234.50	8.700%	$254.9015	$254.90	$254.90	$254.90
Purchase #6	$38.96	13.479%	$44.2114	$44.21	$44.20	$44.20
Purchase #7	$113.47	12.760%	$127.9488	$127.95	$127.95	$127.90
7 purchase totals =	$783.82		$844.7097	$844.70	$844.70	$844.70