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	$21.98	12.688%	$24.7688	$24.77	$24.75	$24.80
Purchase #2	$130.39	11.536%	$145.4318	$145.43	$145.45	$145.40
Purchase #3	$168.67	9.400%	$184.525	$184.53	$184.55	$184.50
Purchase #4	$49.82	8.336%	$53.973	$53.97	$53.95	$54.00
Purchase #5	$75.70	9.831%	$83.1421	$83.14	$83.15	$83.10
Purchase #6	$63.94	13.339%	$72.469	$72.47	$72.45	$72.50
Purchase #7	$176.41	13.537%	$200.2906	$200.29	$200.30	$200.30
7 purchase totals =	$686.91		$764.6003	$764.60	$764.60	$764.60