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	$62.83	6.439%	$66.8756	$66.88	$66.90	$66.90
Purchase #2	$143.86	4.466%	$150.2848	$150.28	$150.30	$150.30
Purchase #3	$225.43	13.268%	$255.3401	$255.34	$255.35	$255.30
Purchase #4	$121.70	8.162%	$131.6332	$131.63	$131.65	$131.60
Purchase #5	$199.86	7.179%	$214.2079	$214.21	$214.20	$214.20
Purchase #6	$30.74	7.174%	$32.9453	$32.95	$32.95	$32.90
Purchase #7	$68.66	3.739%	$71.2272	$71.23	$71.25	$71.20
7 purchase totals =	$853.08		$922.5141	$922.52	$922.60	$922.40