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	$43.85	10.594%	$48.4955	$48.50	$48.50	$48.50
Purchase #2	$39.27	7.637%	$42.269	$42.27	$42.25	$42.30
Purchase #3	$229.91	9.874%	$252.6113	$252.61	$252.60	$252.60
Purchase #4	$59.37	8.772%	$64.5779	$64.58	$64.60	$64.60
Purchase #5	$16.37	8.812%	$17.8125	$17.81	$17.80	$17.80
Purchase #6	$75.77	6.388%	$80.6102	$80.61	$80.60	$80.60
Purchase #7	$79.99	11.597%	$89.2664	$89.27	$89.25	$89.30
7 purchase totals =	$544.53		$595.6428	$595.65	$595.60	$595.70