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	$41.65	9.281%	$45.5155	$45.52	$45.50	$45.50
Purchase #2	$59.78	10.714%	$66.1848	$66.18	$66.20	$66.20
Purchase #3	$63.65	4.584%	$66.5677	$66.57	$66.55	$66.60
Purchase #4	$17.48	11.826%	$19.5472	$19.55	$19.55	$19.50
Purchase #5	$104.30	12.151%	$116.9735	$116.97	$116.95	$117.00
Purchase #6	$7.28	6.323%	$7.7403	$7.74	$7.75	$7.70
Purchase #7	$16.63	11.462%	$18.5361	$18.54	$18.55	$18.50
7 purchase totals =	$310.77		$341.0651	$341.07	$341.05	$341.00