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	$145.96	7.306%	$156.6238	$156.62	$156.60	$156.60
Purchase #2	$31.27	13.805%	$35.5868	$35.59	$35.60	$35.60
Purchase #3	$24.79	11.300%	$27.5913	$27.59	$27.60	$27.60
Purchase #4	$53.71	4.346%	$56.0442	$56.04	$56.05	$56.00
Purchase #5	$133.73	5.749%	$141.4181	$141.42	$141.40	$141.40
Purchase #6	$142.82	13.484%	$162.0778	$162.08	$162.10	$162.10
Purchase #7	$56.78	6.736%	$60.6047	$60.60	$60.60	$60.60
7 purchase totals =	$589.06		$639.9467	$639.94	$639.95	$639.90