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	$169.44	6.581%	$180.5908	$180.59	$180.60	$180.60
Purchase #2	$229.60	5.328%	$241.8331	$241.83	$241.85	$241.80
Purchase #3	$92.50	13.343%	$104.8423	$104.84	$104.85	$104.80
Purchase #4	$55.58	11.829%	$62.1546	$62.15	$62.15	$62.20
Purchase #5	$93.94	9.429%	$102.7976	$102.80	$102.80	$102.80
Purchase #6	$152.75	12.253%	$171.4665	$171.47	$171.45	$171.50
Purchase #7	$196.75	9.230%	$214.91	$214.91	$214.90	$214.90
7 purchase totals =	$990.56		$1,078.5949	$1,078.59	$1,078.60	$1,078.60