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	$134.37	7.449%	$144.3792	$144.38	$144.40	$144.40
Purchase #2	$68.85	13.372%	$78.0566	$78.06	$78.05	$78.10
Purchase #3	$232.97	9.809%	$255.822	$255.82	$255.80	$255.80
Purchase #4	$214.38	5.394%	$225.9437	$225.94	$225.95	$225.90
Purchase #5	$89.88	8.227%	$97.2744	$97.27	$97.25	$97.30
Purchase #6	$179.55	6.317%	$190.8922	$190.89	$190.90	$190.90
Purchase #7	$51.27	3.748%	$53.1916	$53.19	$53.20	$53.20
7 purchase totals =	$971.27		$1,045.5597	$1,045.55	$1,045.55	$1,045.60