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	$67.86	12.477%	$76.3269	$76.33	$76.35	$76.30
Purchase #2	$250.83	11.478%	$279.6203	$279.62	$279.60	$279.60
Purchase #3	$162.46	10.576%	$179.6418	$179.64	$179.65	$179.60
Purchase #4	$72.83	9.376%	$79.6585	$79.66	$79.65	$79.70
Purchase #5	$166.69	3.406%	$172.3675	$172.37	$172.35	$172.40
Purchase #6	$124.60	4.443%	$130.136	$130.14	$130.15	$130.10
Purchase #7	$106.40	8.570%	$115.5185	$115.52	$115.50	$115.50
7 purchase totals =	$951.67		$1,033.2695	$1,033.28	$1,033.25	$1,033.20