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	$48.87	8.863%	$53.2013	$53.20	$53.20	$53.20
Purchase #2	$175.45	6.762%	$187.3139	$187.31	$187.30	$187.30
Purchase #3	$29.56	11.157%	$32.858	$32.86	$32.85	$32.90
Purchase #4	$95.66	8.602%	$103.8887	$103.89	$103.90	$103.90
Purchase #5	$175.41	7.582%	$188.7096	$188.71	$188.70	$188.70
Purchase #6	$56.51	11.261%	$62.8736	$62.87	$62.85	$62.90
Purchase #7	$216.56	5.312%	$228.0637	$228.06	$228.05	$228.10
7 purchase totals =	$798.02		$856.9088	$856.90	$856.85	$857.00