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	$229.52	11.766%	$256.5253	$256.53	$256.55	$256.50
Purchase #2	$72.62	6.777%	$77.5415	$77.54	$77.55	$77.50
Purchase #3	$172.56	8.757%	$187.6711	$187.67	$187.65	$187.70
Purchase #4	$196.82	7.503%	$211.5874	$211.59	$211.60	$211.60
Purchase #5	$165.86	4.847%	$173.8992	$173.90	$173.90	$173.90
Purchase #6	$122.87	5.666%	$129.8318	$129.83	$129.85	$129.80
Purchase #7	$71.40	9.737%	$78.3522	$78.35	$78.35	$78.40
7 purchase totals =	$1,031.65		$1,115.4085	$1,115.41	$1,115.45	$1,115.40