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	$13.65	13.667%	$15.5155	$15.52	$15.50	$15.50
Purchase #2	$146.68	10.181%	$161.6135	$161.61	$161.60	$161.60
Purchase #3	$221.47	12.124%	$248.321	$248.32	$248.30	$248.30
Purchase #4	$36.55	9.394%	$39.9835	$39.98	$40.00	$40.00
Purchase #5	$108.86	3.236%	$112.3827	$112.38	$112.40	$112.40
Purchase #6	$205.81	7.123%	$220.4698	$220.47	$220.45	$220.50
Purchase #7	$213.41	4.457%	$222.9217	$222.92	$222.90	$222.90
7 purchase totals =	$946.43		$1,021.2077	$1,021.20	$1,021.15	$1,021.20