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	$51.52	8.585%	$55.943	$55.94	$55.95	$55.90
Purchase #2	$241.69	12.702%	$272.3895	$272.39	$272.40	$272.40
Purchase #3	$100.87	11.151%	$112.118	$112.12	$112.10	$112.10
Purchase #4	$106.85	5.639%	$112.8753	$112.88	$112.90	$112.90
Purchase #5	$233.34	13.646%	$265.1816	$265.18	$265.20	$265.20
Purchase #6	$107.56	6.440%	$114.4869	$114.49	$114.50	$114.50
Purchase #7	$145.70	3.272%	$150.4673	$150.47	$150.45	$150.50
7 purchase totals =	$987.53		$1,083.4616	$1,083.47	$1,083.50	$1,083.50