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	$150.30	3.445%	$155.4778	$155.48	$155.50	$155.50
Purchase #2	$50.75	7.813%	$54.7151	$54.72	$54.70	$54.70
Purchase #3	$228.43	3.451%	$236.3131	$236.31	$236.30	$236.30
Purchase #4	$118.89	12.294%	$133.5063	$133.51	$133.50	$133.50
Purchase #5	$72.97	11.849%	$81.6162	$81.62	$81.60	$81.60
Purchase #6	$52.38	12.749%	$59.0579	$59.06	$59.05	$59.10
Purchase #7	$172.85	7.824%	$186.3738	$186.37	$186.35	$186.40
7 purchase totals =	$846.57		$907.0602	$907.07	$907.00	$907.10