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	$201.71	12.286%	$226.4921	$226.49	$226.50	$226.50
Purchase #2	$37.88	9.380%	$41.4331	$41.43	$41.45	$41.40
Purchase #3	$65.50	3.685%	$67.9137	$67.91	$67.90	$67.90
Purchase #4	$38.37	4.652%	$40.155	$40.16	$40.15	$40.20
Purchase #5	$228.77	13.255%	$259.0935	$259.09	$259.10	$259.10
Purchase #6	$58.89	12.188%	$66.0675	$66.07	$66.05	$66.10
Purchase #7	$134.79	12.658%	$151.8517	$151.85	$151.85	$151.90
7 purchase totals =	$765.91		$853.0066	$853.00	$853.00	$853.10