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	$222.37	13.815%	$253.0904	$253.09	$253.10	$253.10
Purchase #2	$74.35	10.144%	$81.8921	$81.89	$81.90	$81.90
Purchase #3	$186.76	7.557%	$200.8735	$200.87	$200.85	$200.90
Purchase #4	$244.69	11.343%	$272.4452	$272.45	$272.45	$272.40
Purchase #5	$169.67	9.326%	$185.4934	$185.49	$185.50	$185.50
Purchase #6	$196.49	9.397%	$214.9542	$214.95	$214.95	$215.00
Purchase #7	$160.43	13.343%	$181.8362	$181.84	$181.85	$181.80
7 purchase totals =	$1,254.76		$1,390.5850	$1,390.58	$1,390.60	$1,390.60