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	$246.90	13.730%	$280.7994	$280.80	$280.80	$280.80
Purchase #2	$18.27	3.649%	$18.9367	$18.94	$18.95	$18.90
Purchase #3	$116.60	13.603%	$132.4611	$132.46	$132.45	$132.50
Purchase #4	$157.43	11.742%	$175.9154	$175.92	$175.90	$175.90
Purchase #5	$137.28	11.169%	$152.6128	$152.61	$152.60	$152.60
Purchase #6	$59.94	8.221%	$64.8677	$64.87	$64.85	$64.90
Purchase #7	$250.68	13.325%	$284.0831	$284.08	$284.10	$284.10
7 purchase totals =	$987.10		$1,109.6762	$1,109.68	$1,109.65	$1,109.70