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	$229.64	6.506%	$244.5804	$244.58	$244.60	$244.60
Purchase #2	$140.87	4.262%	$146.8739	$146.87	$146.85	$146.90
Purchase #3	$51.42	5.204%	$54.0959	$54.10	$54.10	$54.10
Purchase #4	$74.75	12.293%	$83.939	$83.94	$83.95	$83.90
Purchase #5	$44.45	13.188%	$50.3121	$50.31	$50.30	$50.30
Purchase #6	$43.84	10.419%	$48.4077	$48.41	$48.40	$48.40
Purchase #7	$135.63	12.467%	$152.539	$152.54	$152.55	$152.50
7 purchase totals =	$720.60		$780.7480	$780.75	$780.75	$780.70