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	$17.78	7.337%	$19.0845	$19.08	$19.10	$19.10
Purchase #2	$166.59	5.720%	$176.1189	$176.12	$176.10	$176.10
Purchase #3	$240.63	4.286%	$250.9434	$250.94	$250.95	$250.90
Purchase #4	$69.89	11.843%	$78.1671	$78.17	$78.15	$78.20
Purchase #5	$15.56	8.130%	$16.825	$16.83	$16.85	$16.80
Purchase #6	$205.73	13.387%	$233.2711	$233.27	$233.25	$233.30
Purchase #7	$116.58	13.151%	$131.9114	$131.91	$131.90	$131.90
7 purchase totals =	$832.76		$906.3214	$906.32	$906.30	$906.30