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	$18.30	12.361%	$20.5621	$20.56	$20.55	$20.60
Purchase #2	$191.72	8.659%	$208.321	$208.32	$208.30	$208.30
Purchase #3	$207.56	11.219%	$230.8462	$230.85	$230.85	$230.80
Purchase #4	$143.65	12.694%	$161.8849	$161.88	$161.90	$161.90
Purchase #5	$196.66	6.163%	$208.7802	$208.78	$208.80	$208.80
Purchase #6	$31.98	13.510%	$36.3005	$36.30	$36.30	$36.30
Purchase #7	$106.58	4.378%	$111.2461	$111.25	$111.25	$111.20
7 purchase totals =	$896.45		$977.9410	$977.94	$977.95	$977.90