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	$80.52	3.502%	$83.3398	$83.34	$83.35	$83.30
Purchase #2	$41.33	12.693%	$46.576	$46.58	$46.60	$46.60
Purchase #3	$146.41	13.808%	$166.6263	$166.63	$166.65	$166.60
Purchase #4	$160.65	9.402%	$175.7543	$175.75	$175.75	$175.80
Purchase #5	$80.86	11.644%	$90.2753	$90.28	$90.30	$90.30
Purchase #6	$18.87	12.208%	$21.1736	$21.17	$21.15	$21.20
Purchase #7	$51.80	5.770%	$54.7889	$54.79	$54.80	$54.80
7 purchase totals =	$580.44		$638.5342	$638.54	$638.60	$638.60