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	$240.58	13.188%	$272.3077	$272.31	$272.30	$272.30
Purchase #2	$82.50	8.466%	$89.4845	$89.48	$89.50	$89.50
Purchase #3	$220.95	6.304%	$234.8787	$234.88	$234.90	$234.90
Purchase #4	$65.64	3.838%	$68.1593	$68.16	$68.15	$68.20
Purchase #5	$206.45	12.667%	$232.601	$232.60	$232.60	$232.60
Purchase #6	$27.58	4.739%	$28.887	$28.89	$28.90	$28.90
Purchase #7	$48.89	5.433%	$51.5462	$51.55	$51.55	$51.50
7 purchase totals =	$892.59		$977.8644	$977.87	$977.90	$977.90