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	$133.59	9.766%	$146.6364	$146.64	$146.65	$146.60
Purchase #2	$242.50	6.732%	$258.8251	$258.83	$258.85	$258.80
Purchase #3	$37.69	7.160%	$40.3886	$40.39	$40.40	$40.40
Purchase #4	$118.46	8.202%	$128.1761	$128.18	$128.20	$128.20
Purchase #5	$82.39	7.149%	$88.2801	$88.28	$88.30	$88.30
Purchase #6	$17.40	10.599%	$19.2442	$19.24	$19.25	$19.20
Purchase #7	$59.83	3.377%	$61.8505	$61.85	$61.85	$61.90
7 purchase totals =	$691.86		$743.4010	$743.41	$743.50	$743.40