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	$13.93	6.717%	$14.8657	$14.87	$14.85	$14.90
Purchase #2	$152.29	4.128%	$158.5765	$158.58	$158.60	$158.60
Purchase #3	$114.77	9.721%	$125.9268	$125.93	$125.95	$125.90
Purchase #4	$241.90	12.850%	$272.9842	$272.98	$273.00	$273.00
Purchase #5	$247.69	7.179%	$265.4717	$265.47	$265.45	$265.50
Purchase #6	$98.65	13.697%	$112.1621	$112.16	$112.15	$112.20
Purchase #7	$216.33	7.167%	$231.8344	$231.83	$231.85	$231.80
7 purchase totals =	$1,085.56		$1,181.8214	$1,181.82	$1,181.85	$1,181.90