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	$163.81	9.351%	$179.1279	$179.13	$179.15	$179.10
Purchase #2	$123.70	8.514%	$134.2318	$134.23	$134.25	$134.20
Purchase #3	$90.45	12.244%	$101.5247	$101.52	$101.50	$101.50
Purchase #4	$64.42	13.227%	$72.9408	$72.94	$72.95	$72.90
Purchase #5	$21.94	11.555%	$24.4752	$24.48	$24.50	$24.50
Purchase #6	$250.70	8.184%	$271.2173	$271.22	$271.20	$271.20
Purchase #7	$241.33	3.534%	$249.8586	$249.86	$249.85	$249.90
7 purchase totals =	$956.35		$1,033.3763	$1,033.38	$1,033.40	$1,033.30