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	$77.28	5.739%	$81.7151	$81.72	$81.70	$81.70
Purchase #2	$150.50	12.716%	$169.6376	$169.64	$169.65	$169.60
Purchase #3	$137.78	5.472%	$145.3193	$145.32	$145.30	$145.30
Purchase #4	$48.33	7.777%	$52.0886	$52.09	$52.10	$52.10
Purchase #5	$50.79	5.356%	$53.5103	$53.51	$53.50	$53.50
Purchase #6	$134.56	6.735%	$143.6226	$143.62	$143.60	$143.60
Purchase #7	$62.76	13.777%	$71.4064	$71.41	$71.40	$71.40
7 purchase totals =	$662.00		$717.2999	$717.31	$717.25	$717.20