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	$6.58	7.636%	$7.0824	$7.08	$7.10	$7.10
Purchase #2	$235.31	8.661%	$255.6902	$255.69	$255.70	$255.70
Purchase #3	$105.48	10.471%	$116.5248	$116.52	$116.50	$116.50
Purchase #4	$207.65	7.554%	$223.3359	$223.34	$223.35	$223.30
Purchase #5	$132.88	6.173%	$141.0827	$141.08	$141.10	$141.10
Purchase #6	$109.71	8.333%	$118.8521	$118.85	$118.85	$118.90
Purchase #7	$45.30	12.826%	$51.1102	$51.11	$51.10	$51.10
7 purchase totals =	$842.91		$913.6783	$913.67	$913.70	$913.70