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	$32.92	10.287%	$36.3065	$36.31	$36.30	$36.30
Purchase #2	$46.25	3.104%	$47.6856	$47.69	$47.70	$47.70
Purchase #3	$151.54	10.750%	$167.8306	$167.83	$167.85	$167.80
Purchase #4	$14.69	5.580%	$15.5097	$15.51	$15.50	$15.50
Purchase #5	$118.60	10.872%	$131.4942	$131.49	$131.50	$131.50
Purchase #6	$125.43	8.771%	$136.4315	$136.43	$136.45	$136.40
Purchase #7	$250.35	7.441%	$268.9785	$268.98	$269.00	$269.00
7 purchase totals =	$739.78		$804.2366	$804.24	$804.30	$804.20