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	$103.38	8.180%	$111.8365	$111.84	$111.85	$111.80
Purchase #2	$197.75	12.184%	$221.8439	$221.84	$221.85	$221.80
Purchase #3	$133.58	9.602%	$146.4064	$146.41	$146.40	$146.40
Purchase #4	$25.93	11.565%	$28.9288	$28.93	$28.95	$28.90
Purchase #5	$166.52	9.753%	$182.7607	$182.76	$182.75	$182.80
Purchase #6	$224.64	13.797%	$255.6336	$255.63	$255.65	$255.60
Purchase #7	$231.75	13.109%	$262.1301	$262.13	$262.15	$262.10
7 purchase totals =	$1,083.55		$1,209.5400	$1,209.54	$1,209.60	$1,209.40