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	$101.45	9.489%	$111.0766	$111.08	$111.10	$111.10
Purchase #2	$143.52	7.518%	$154.3098	$154.31	$154.30	$154.30
Purchase #3	$126.96	5.228%	$133.5975	$133.60	$133.60	$133.60
Purchase #4	$103.76	8.184%	$112.2517	$112.25	$112.25	$112.30
Purchase #5	$36.41	10.300%	$40.1602	$40.16	$40.15	$40.20
Purchase #6	$91.33	12.169%	$102.4439	$102.44	$102.45	$102.40
Purchase #7	$59.71	13.261%	$67.6281	$67.63	$67.65	$67.60
7 purchase totals =	$663.14		$721.4678	$721.47	$721.50	$721.50