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	$69.58	5.693%	$73.5412	$73.54	$73.55	$73.50
Purchase #2	$46.86	11.343%	$52.1753	$52.18	$52.20	$52.20
Purchase #3	$16.54	7.500%	$17.7805	$17.78	$17.80	$17.80
Purchase #4	$116.32	6.255%	$123.5958	$123.60	$123.60	$123.60
Purchase #5	$244.50	13.474%	$277.4439	$277.44	$277.45	$277.40
Purchase #6	$78.27	9.779%	$85.924	$85.92	$85.90	$85.90
Purchase #7	$104.48	4.752%	$109.4449	$109.44	$109.45	$109.40
7 purchase totals =	$676.55		$739.9056	$739.90	$739.95	$739.80