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	$97.37	9.331%	$106.4556	$106.46	$106.45	$106.50
Purchase #2	$144.68	4.859%	$151.71	$151.71	$151.70	$151.70
Purchase #3	$104.36	13.579%	$118.531	$118.53	$118.55	$118.50
Purchase #4	$112.29	13.520%	$127.4716	$127.47	$127.45	$127.50
Purchase #5	$61.42	13.622%	$69.7866	$69.79	$69.80	$69.80
Purchase #6	$121.44	9.200%	$132.6125	$132.61	$132.60	$132.60
Purchase #7	$50.68	6.268%	$53.8566	$53.86	$53.85	$53.90
7 purchase totals =	$692.24		$760.4239	$760.43	$760.40	$760.50