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	$155.58	6.806%	$166.1688	$166.17	$166.15	$166.20
Purchase #2	$71.85	11.452%	$80.0783	$80.08	$80.10	$80.10
Purchase #3	$243.83	4.694%	$255.2754	$255.28	$255.30	$255.30
Purchase #4	$158.27	10.492%	$174.8757	$174.88	$174.90	$174.90
Purchase #5	$47.84	12.753%	$53.941	$53.94	$53.95	$53.90
Purchase #6	$20.45	3.868%	$21.241	$21.24	$21.25	$21.20
Purchase #7	$33.79	13.864%	$38.4746	$38.47	$38.45	$38.50
7 purchase totals =	$731.61		$790.0548	$790.06	$790.10	$790.10