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	$36.32	8.120%	$39.2692	$39.27	$39.25	$39.30
Purchase #2	$108.41	3.193%	$111.8715	$111.87	$111.85	$111.90
Purchase #3	$238.75	4.455%	$249.3863	$249.39	$249.40	$249.40
Purchase #4	$211.37	6.525%	$225.1619	$225.16	$225.15	$225.20
Purchase #5	$89.37	9.518%	$97.8762	$97.88	$97.90	$97.90
Purchase #6	$176.68	11.126%	$196.3374	$196.34	$196.35	$196.30
Purchase #7	$70.77	5.678%	$74.7883	$74.79	$74.80	$74.80
7 purchase totals =	$931.67		$994.6908	$994.70	$994.70	$994.80