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	$166.85	7.260%	$178.9633	$178.96	$178.95	$179.00
Purchase #2	$60.41	9.812%	$66.3374	$66.34	$66.35	$66.30
Purchase #3	$127.92	10.860%	$141.8121	$141.81	$141.80	$141.80
Purchase #4	$90.56	12.409%	$101.7976	$101.80	$101.80	$101.80
Purchase #5	$172.61	10.552%	$190.8238	$190.82	$190.80	$190.80
Purchase #6	$86.59	3.110%	$89.2829	$89.28	$89.30	$89.30
Purchase #7	$15.98	9.348%	$17.4738	$17.47	$17.45	$17.50
7 purchase totals =	$720.92		$786.4909	$786.48	$786.45	$786.50