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	$51.28	12.349%	$57.6126	$57.61	$57.60	$57.60
Purchase #2	$184.31	12.509%	$207.3653	$207.37	$207.35	$207.40
Purchase #3	$167.28	11.209%	$186.0304	$186.03	$186.05	$186.00
Purchase #4	$208.56	11.139%	$231.7915	$231.79	$231.80	$231.80
Purchase #5	$157.78	10.647%	$174.5788	$174.58	$174.60	$174.60
Purchase #6	$157.31	6.782%	$167.9788	$167.98	$168.00	$168.00
Purchase #7	$153.90	13.746%	$175.0551	$175.06	$175.05	$175.10
7 purchase totals =	$1,080.42		$1,200.4125	$1,200.42	$1,200.45	$1,200.50