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	$238.94	4.431%	$249.5274	$249.53	$249.55	$249.50
Purchase #2	$180.82	7.769%	$194.8679	$194.87	$194.85	$194.90
Purchase #3	$132.56	13.394%	$150.3151	$150.32	$150.30	$150.30
Purchase #4	$73.82	11.683%	$82.4444	$82.44	$82.45	$82.40
Purchase #5	$155.80	13.158%	$176.3002	$176.30	$176.30	$176.30
Purchase #6	$233.86	6.647%	$249.4047	$249.40	$249.40	$249.40
Purchase #7	$145.61	3.153%	$150.2011	$150.20	$150.20	$150.20
7 purchase totals =	$1,161.41		$1,253.0608	$1,253.06	$1,253.05	$1,253.00