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	$78.99	12.181%	$88.6118	$88.61	$88.60	$88.60
Purchase #2	$230.69	7.494%	$247.9779	$247.98	$248.00	$248.00
Purchase #3	$83.95	8.193%	$90.828	$90.83	$90.85	$90.80
Purchase #4	$36.28	4.186%	$37.7987	$37.80	$37.80	$37.80
Purchase #5	$234.62	12.692%	$264.398	$264.40	$264.40	$264.40
Purchase #6	$151.76	10.599%	$167.845	$167.85	$167.85	$167.80
Purchase #7	$105.27	12.646%	$118.5824	$118.58	$118.60	$118.60
7 purchase totals =	$921.56		$1,016.0418	$1,016.05	$1,016.10	$1,016.00