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	$118.51	11.624%	$132.2856	$132.29	$132.30	$132.30
Purchase #2	$239.57	3.797%	$248.6665	$248.67	$248.65	$248.70
Purchase #3	$162.77	10.250%	$179.4539	$179.45	$179.45	$179.50
Purchase #4	$68.49	3.674%	$71.0063	$71.01	$71.00	$71.00
Purchase #5	$129.88	12.734%	$146.4189	$146.42	$146.40	$146.40
Purchase #6	$175.61	11.658%	$196.0826	$196.08	$196.10	$196.10
Purchase #7	$14.91	6.137%	$15.825	$15.83	$15.85	$15.80
7 purchase totals =	$909.74		$989.7388	$989.75	$989.75	$989.80