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	$236.51	7.622%	$254.5368	$254.54	$254.55	$254.50
Purchase #2	$70.27	11.103%	$78.0721	$78.07	$78.05	$78.10
Purchase #3	$56.60	4.439%	$59.1125	$59.11	$59.10	$59.10
Purchase #4	$45.39	10.349%	$50.0874	$50.09	$50.10	$50.10
Purchase #5	$27.93	3.764%	$28.9813	$28.98	$29.00	$29.00
Purchase #6	$185.62	3.544%	$192.1984	$192.20	$192.20	$192.20
Purchase #7	$167.32	8.360%	$181.308	$181.31	$181.30	$181.30
7 purchase totals =	$789.64		$844.2965	$844.30	$844.30	$844.30