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	$151.38	13.851%	$172.3476	$172.35	$172.35	$172.30
Purchase #2	$87.36	3.737%	$90.6246	$90.62	$90.60	$90.60
Purchase #3	$224.74	3.168%	$231.8598	$231.86	$231.85	$231.90
Purchase #4	$146.50	5.396%	$154.4051	$154.41	$154.40	$154.40
Purchase #5	$49.81	5.535%	$52.567	$52.57	$52.55	$52.60
Purchase #6	$150.65	6.224%	$160.0265	$160.03	$160.05	$160.00
Purchase #7	$99.89	8.512%	$108.3926	$108.39	$108.40	$108.40
7 purchase totals =	$910.33		$970.2232	$970.23	$970.20	$970.20