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	$34.90	9.523%	$38.2235	$38.22	$38.20	$38.20
Purchase #2	$150.57	5.218%	$158.4267	$158.43	$158.45	$158.40
Purchase #3	$29.75	11.812%	$33.2641	$33.26	$33.25	$33.30
Purchase #4	$94.35	4.833%	$98.9099	$98.91	$98.90	$98.90
Purchase #5	$49.55	3.218%	$51.1445	$51.14	$51.15	$51.10
Purchase #6	$65.56	11.256%	$72.9394	$72.94	$72.95	$72.90
Purchase #7	$161.25	6.244%	$171.3185	$171.32	$171.30	$171.30
7 purchase totals =	$585.93		$624.2266	$624.22	$624.20	$624.10