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	$162.99	6.508%	$173.5974	$173.60	$173.60	$173.60
Purchase #2	$246.82	13.811%	$280.9083	$280.91	$280.90	$280.90
Purchase #3	$227.79	7.175%	$244.1339	$244.13	$244.15	$244.10
Purchase #4	$122.88	13.763%	$139.792	$139.79	$139.80	$139.80
Purchase #5	$48.50	12.649%	$54.6348	$54.63	$54.65	$54.60
Purchase #6	$132.81	10.272%	$146.4522	$146.45	$146.45	$146.50
Purchase #7	$242.47	3.401%	$250.7164	$250.72	$250.70	$250.70
7 purchase totals =	$1,184.26		$1,290.2350	$1,290.23	$1,290.25	$1,290.20