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	$56.72	13.633%	$64.4526	$64.45	$64.45	$64.50
Purchase #2	$129.56	12.793%	$146.1346	$146.13	$146.15	$146.10
Purchase #3	$41.70	9.470%	$45.649	$45.65	$45.65	$45.60
Purchase #4	$75.82	3.760%	$78.6708	$78.67	$78.65	$78.70
Purchase #5	$31.71	8.834%	$34.5113	$34.51	$34.50	$34.50
Purchase #6	$144.29	11.218%	$160.4765	$160.48	$160.50	$160.50
Purchase #7	$112.44	12.750%	$126.7761	$126.78	$126.80	$126.80
7 purchase totals =	$592.24		$656.6709	$656.67	$656.70	$656.70