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	$151.54	4.602%	$158.5139	$158.51	$158.50	$158.50
Purchase #2	$124.90	7.420%	$134.1676	$134.17	$134.15	$134.20
Purchase #3	$73.90	13.159%	$83.6245	$83.62	$83.60	$83.60
Purchase #4	$80.31	6.581%	$85.5952	$85.60	$85.60	$85.60
Purchase #5	$168.83	9.637%	$185.1001	$185.10	$185.10	$185.10
Purchase #6	$114.33	12.562%	$128.6921	$128.69	$128.70	$128.70
Purchase #7	$191.62	10.353%	$211.4584	$211.46	$211.45	$211.50
7 purchase totals =	$905.43		$987.1518	$987.15	$987.10	$987.20