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	$39.92	13.491%	$45.3056	$45.31	$45.30	$45.30
Purchase #2	$139.75	10.819%	$154.8696	$154.87	$154.85	$154.90
Purchase #3	$208.35	12.708%	$234.8271	$234.83	$234.85	$234.80
Purchase #4	$94.47	6.647%	$100.7494	$100.75	$100.75	$100.70
Purchase #5	$105.76	12.353%	$118.8245	$118.82	$118.80	$118.80
Purchase #6	$200.91	11.587%	$224.1894	$224.19	$224.20	$224.20
Purchase #7	$64.95	3.301%	$67.094	$67.09	$67.10	$67.10
7 purchase totals =	$854.11		$945.8596	$945.86	$945.85	$945.80