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	$93.59	10.571%	$103.4834	$103.48	$103.50	$103.50
Purchase #2	$160.80	13.104%	$181.8712	$181.87	$181.85	$181.90
Purchase #3	$38.83	7.136%	$41.6009	$41.60	$41.60	$41.60
Purchase #4	$10.92	7.584%	$11.7482	$11.75	$11.75	$11.70
Purchase #5	$205.52	8.177%	$222.3254	$222.33	$222.35	$222.30
Purchase #6	$68.37	11.630%	$76.3214	$76.32	$76.30	$76.30
Purchase #7	$124.92	13.600%	$141.9091	$141.91	$141.90	$141.90
7 purchase totals =	$702.95		$779.2596	$779.26	$779.25	$779.20