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	$42.75	7.287%	$45.8652	$45.87	$45.85	$45.90
Purchase #2	$203.94	5.732%	$215.6298	$215.63	$215.65	$215.60
Purchase #3	$202.89	7.187%	$217.4717	$217.47	$217.45	$217.50
Purchase #4	$148.52	12.622%	$167.2662	$167.27	$167.25	$167.30
Purchase #5	$78.42	12.726%	$88.3997	$88.40	$88.40	$88.40
Purchase #6	$95.95	12.361%	$107.8104	$107.81	$107.80	$107.80
Purchase #7	$36.93	10.501%	$40.808	$40.81	$40.80	$40.80
7 purchase totals =	$809.40		$883.2510	$883.26	$883.20	$883.30