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	$53.66	4.610%	$56.1337	$56.13	$56.15	$56.10
Purchase #2	$86.27	12.533%	$97.0822	$97.08	$97.10	$97.10
Purchase #3	$80.85	10.705%	$89.505	$89.51	$89.50	$89.50
Purchase #4	$192.48	12.569%	$216.6728	$216.67	$216.65	$216.70
Purchase #5	$54.48	9.852%	$59.8474	$59.85	$59.85	$59.80
Purchase #6	$53.98	7.783%	$58.1813	$58.18	$58.20	$58.20
Purchase #7	$20.62	7.252%	$22.1154	$22.12	$22.10	$22.10
7 purchase totals =	$542.34		$599.5378	$599.54	$599.55	$599.50