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	$39.93	6.199%	$42.4053	$42.41	$42.40	$42.40
Purchase #2	$33.49	12.201%	$37.5761	$37.58	$37.60	$37.60
Purchase #3	$40.52	5.118%	$42.5938	$42.59	$42.60	$42.60
Purchase #4	$11.27	10.868%	$12.4948	$12.49	$12.50	$12.50
Purchase #5	$144.83	10.164%	$159.5505	$159.55	$159.55	$159.60
Purchase #6	$162.88	6.752%	$173.8777	$173.88	$173.90	$173.90
Purchase #7	$32.88	7.334%	$35.2914	$35.29	$35.30	$35.30
7 purchase totals =	$465.80		$503.7896	$503.79	$503.85	$503.90