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	$38.75	4.726%	$40.5813	$40.58	$40.60	$40.60
Purchase #2	$133.59	9.451%	$146.2156	$146.22	$146.20	$146.20
Purchase #3	$37.85	8.614%	$41.1104	$41.11	$41.10	$41.10
Purchase #4	$206.52	12.443%	$232.2173	$232.22	$232.20	$232.20
Purchase #5	$214.77	9.307%	$234.7586	$234.76	$234.75	$234.80
Purchase #6	$104.92	11.836%	$117.3383	$117.34	$117.35	$117.30
Purchase #7	$82.89	8.410%	$89.861	$89.86	$89.85	$89.90
7 purchase totals =	$819.29		$902.0825	$902.09	$902.05	$902.10