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	$91.50	10.258%	$100.8861	$100.89	$100.90	$100.90
Purchase #2	$127.34	5.508%	$134.3539	$134.35	$134.35	$134.40
Purchase #3	$187.94	13.767%	$213.8137	$213.81	$213.80	$213.80
Purchase #4	$22.81	4.667%	$23.8745	$23.87	$23.85	$23.90
Purchase #5	$9.81	11.370%	$10.9254	$10.93	$10.95	$10.90
Purchase #6	$115.46	6.822%	$123.3367	$123.34	$123.35	$123.30
Purchase #7	$154.59	6.868%	$165.2072	$165.21	$165.20	$165.20
7 purchase totals =	$709.45		$772.3975	$772.40	$772.40	$772.40