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	$26.50	5.242%	$27.8891	$27.89	$27.90	$27.90
Purchase #2	$122.25	3.599%	$126.6498	$126.65	$126.65	$126.60
Purchase #3	$55.56	7.561%	$59.7609	$59.76	$59.75	$59.80
Purchase #4	$92.30	6.707%	$98.4906	$98.49	$98.50	$98.50
Purchase #5	$108.30	10.789%	$119.9845	$119.98	$120.00	$120.00
Purchase #6	$74.27	8.780%	$80.7909	$80.79	$80.80	$80.80
Purchase #7	$45.32	3.103%	$46.7263	$46.73	$46.75	$46.70
7 purchase totals =	$524.50		$560.2921	$560.29	$560.35	$560.30