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	$38.29	11.703%	$42.7711	$42.77	$42.75	$42.80
Purchase #2	$63.27	5.244%	$66.5879	$66.59	$66.60	$66.60
Purchase #3	$151.63	7.229%	$162.5913	$162.59	$162.60	$162.60
Purchase #4	$56.92	9.134%	$62.1191	$62.12	$62.10	$62.10
Purchase #5	$164.63	6.395%	$175.1581	$175.16	$175.15	$175.20
Purchase #6	$16.57	12.125%	$18.5791	$18.58	$18.60	$18.60
Purchase #7	$224.89	6.239%	$238.9209	$238.92	$238.90	$238.90
7 purchase totals =	$716.20		$766.7275	$766.73	$766.70	$766.80