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	$35.81	3.784%	$37.1651	$37.17	$37.15	$37.20
Purchase #2	$127.72	6.775%	$136.373	$136.37	$136.35	$136.40
Purchase #3	$35.72	9.364%	$39.0648	$39.06	$39.05	$39.10
Purchase #4	$192.53	13.816%	$219.1299	$219.13	$219.15	$219.10
Purchase #5	$214.78	5.754%	$227.1384	$227.14	$227.15	$227.10
Purchase #6	$126.89	13.328%	$143.8019	$143.80	$143.80	$143.80
Purchase #7	$37.81	12.603%	$42.5752	$42.58	$42.60	$42.60
7 purchase totals =	$771.26		$845.2483	$845.25	$845.25	$845.30