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	$22.50	8.525%	$24.4181	$24.42	$24.40	$24.40
Purchase #2	$109.77	13.433%	$124.5154	$124.52	$124.50	$124.50
Purchase #3	$100.83	8.255%	$109.1535	$109.15	$109.15	$109.20
Purchase #4	$26.76	6.228%	$28.4266	$28.43	$28.45	$28.40
Purchase #5	$86.77	6.736%	$92.6148	$92.61	$92.60	$92.60
Purchase #6	$145.92	7.111%	$156.2964	$156.30	$156.30	$156.30
Purchase #7	$47.95	12.517%	$53.9519	$53.95	$53.95	$54.00
7 purchase totals =	$540.50		$589.3767	$589.38	$589.35	$589.40