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	$234.41	13.727%	$266.5875	$266.59	$266.60	$266.60
Purchase #2	$43.37	4.726%	$45.4197	$45.42	$45.40	$45.40
Purchase #3	$249.82	11.839%	$279.3962	$279.40	$279.40	$279.40
Purchase #4	$78.65	10.443%	$86.8634	$86.86	$86.85	$86.90
Purchase #5	$110.94	11.482%	$123.6781	$123.68	$123.70	$123.70
Purchase #6	$71.57	7.152%	$76.6887	$76.69	$76.70	$76.70
Purchase #7	$189.68	5.243%	$199.6249	$199.62	$199.60	$199.60
7 purchase totals =	$978.44		$1,078.2585	$1,078.26	$1,078.25	$1,078.30