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	$85.58	5.282%	$90.1003	$90.10	$90.10	$90.10
Purchase #2	$167.95	12.166%	$188.3828	$188.38	$188.40	$188.40
Purchase #3	$206.75	7.712%	$222.6946	$222.69	$222.70	$222.70
Purchase #4	$122.64	12.682%	$138.1932	$138.19	$138.20	$138.20
Purchase #5	$166.80	8.554%	$181.0681	$181.07	$181.05	$181.10
Purchase #6	$35.72	4.857%	$37.4549	$37.45	$37.45	$37.50
Purchase #7	$229.36	11.464%	$255.6538	$255.65	$255.65	$255.70
7 purchase totals =	$1,014.80		$1,113.5477	$1,113.53	$1,113.55	$1,113.70