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	$57.30	10.169%	$63.1268	$63.13	$63.15	$63.10
Purchase #2	$132.80	12.548%	$149.4637	$149.46	$149.45	$149.50
Purchase #3	$35.73	13.368%	$40.5064	$40.51	$40.50	$40.50
Purchase #4	$96.64	9.557%	$105.8759	$105.88	$105.90	$105.90
Purchase #5	$69.33	5.117%	$72.8776	$72.88	$72.90	$72.90
Purchase #6	$140.62	3.854%	$146.0395	$146.04	$146.05	$146.00
Purchase #7	$234.98	12.201%	$263.6499	$263.65	$263.65	$263.60
7 purchase totals =	$767.40		$841.5398	$841.55	$841.60	$841.50