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	$10.88	5.781%	$11.509	$11.51	$11.50	$11.50
Purchase #2	$44.41	11.823%	$49.6606	$49.66	$49.65	$49.70
Purchase #3	$91.63	12.444%	$103.0324	$103.03	$103.05	$103.00
Purchase #4	$130.91	6.250%	$139.0919	$139.09	$139.10	$139.10
Purchase #5	$177.30	10.711%	$196.2906	$196.29	$196.30	$196.30
Purchase #6	$239.86	6.485%	$255.4149	$255.41	$255.40	$255.40
Purchase #7	$20.87	5.727%	$22.0652	$22.07	$22.05	$22.10
7 purchase totals =	$715.86		$777.0646	$777.06	$777.05	$777.10