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	$82.79	6.424%	$88.1084	$88.11	$88.10	$88.10
Purchase #2	$82.43	9.504%	$90.2641	$90.26	$90.25	$90.30
Purchase #3	$197.67	12.401%	$222.1831	$222.18	$222.20	$222.20
Purchase #4	$64.37	12.286%	$72.2785	$72.28	$72.30	$72.30
Purchase #5	$230.65	4.747%	$241.599	$241.60	$241.60	$241.60
Purchase #6	$80.65	6.440%	$85.8439	$85.84	$85.85	$85.80
Purchase #7	$106.52	11.240%	$118.4928	$118.49	$118.50	$118.50
7 purchase totals =	$845.08		$918.7698	$918.76	$918.80	$918.80