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	$229.38	11.433%	$255.605	$255.61	$255.60	$255.60
Purchase #2	$37.33	4.305%	$38.9371	$38.94	$38.95	$38.90
Purchase #3	$54.52	10.645%	$60.3237	$60.32	$60.30	$60.30
Purchase #4	$144.71	9.489%	$158.4415	$158.44	$158.45	$158.40
Purchase #5	$250.93	12.185%	$281.5058	$281.51	$281.50	$281.50
Purchase #6	$26.40	7.646%	$28.4185	$28.42	$28.40	$28.40
Purchase #7	$164.37	6.645%	$175.2924	$175.29	$175.30	$175.30
7 purchase totals =	$907.64		$998.5240	$998.53	$998.50	$998.40