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	$74.31	12.712%	$83.7563	$83.76	$83.75	$83.80
Purchase #2	$58.34	5.839%	$61.7465	$61.75	$61.75	$61.70
Purchase #3	$8.65	13.176%	$9.7897	$9.79	$9.80	$9.80
Purchase #4	$193.25	11.423%	$215.3249	$215.32	$215.30	$215.30
Purchase #5	$101.61	3.499%	$105.1653	$105.17	$105.15	$105.20
Purchase #6	$152.39	4.723%	$159.5874	$159.59	$159.60	$159.60
Purchase #7	$228.85	11.808%	$255.8726	$255.87	$255.85	$255.90
7 purchase totals =	$817.40		$891.2427	$891.25	$891.20	$891.30