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	$38.65	4.855%	$40.5265	$40.53	$40.55	$40.50
Purchase #2	$129.60	6.672%	$138.2469	$138.25	$138.25	$138.20
Purchase #3	$228.81	6.696%	$244.1311	$244.13	$244.15	$244.10
Purchase #4	$126.46	4.739%	$132.4529	$132.45	$132.45	$132.50
Purchase #5	$74.32	7.761%	$80.088	$80.09	$80.10	$80.10
Purchase #6	$223.60	11.812%	$250.0116	$250.01	$250.00	$250.00
Purchase #7	$186.41	5.382%	$196.4426	$196.44	$196.45	$196.40
7 purchase totals =	$1,007.85		$1,081.8996	$1,081.90	$1,081.95	$1,081.80