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	$100.39	11.719%	$112.1547	$112.15	$112.15	$112.20
Purchase #2	$173.73	6.750%	$185.4568	$185.46	$185.45	$185.50
Purchase #3	$131.99	13.685%	$150.0528	$150.05	$150.05	$150.10
Purchase #4	$172.83	6.657%	$184.3353	$184.34	$184.35	$184.30
Purchase #5	$189.61	10.202%	$208.954	$208.95	$208.95	$209.00
Purchase #6	$231.47	11.242%	$257.4919	$257.49	$257.50	$257.50
Purchase #7	$90.25	6.643%	$96.2453	$96.25	$96.25	$96.20
7 purchase totals =	$1,090.27		$1,194.6908	$1,194.69	$1,194.70	$1,194.80