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	$35.58	7.325%	$38.1862	$38.19	$38.20	$38.20
Purchase #2	$127.51	13.336%	$144.5147	$144.51	$144.50	$144.50
Purchase #3	$115.88	13.813%	$131.8865	$131.89	$131.90	$131.90
Purchase #4	$70.70	10.371%	$78.0323	$78.03	$78.05	$78.00
Purchase #5	$144.51	11.733%	$161.4654	$161.47	$161.45	$161.50
Purchase #6	$171.87	8.572%	$186.6027	$186.60	$186.60	$186.60
Purchase #7	$20.83	8.345%	$22.5683	$22.57	$22.55	$22.60
7 purchase totals =	$686.88		$763.2561	$763.26	$763.25	$763.30