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	$122.59	13.604%	$139.2671	$139.27	$139.25	$139.30
Purchase #2	$80.90	11.725%	$90.3855	$90.39	$90.40	$90.40
Purchase #3	$211.56	9.521%	$231.7026	$231.70	$231.70	$231.70
Purchase #4	$86.31	4.188%	$89.9247	$89.92	$89.90	$89.90
Purchase #5	$45.45	13.697%	$51.6753	$51.68	$51.70	$51.70
Purchase #6	$90.37	3.111%	$93.1814	$93.18	$93.20	$93.20
Purchase #7	$233.32	7.311%	$250.378	$250.38	$250.40	$250.40
7 purchase totals =	$870.50		$946.5146	$946.52	$946.55	$946.60