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	$20.65	10.838%	$22.888	$22.89	$22.90	$22.90
Purchase #2	$222.98	4.495%	$233.003	$233.00	$233.00	$233.00
Purchase #3	$117.51	11.623%	$131.1682	$131.17	$131.15	$131.20
Purchase #4	$57.77	8.228%	$62.5233	$62.52	$62.50	$62.50
Purchase #5	$94.27	13.435%	$106.9352	$106.94	$106.95	$106.90
Purchase #6	$75.59	12.852%	$85.3048	$85.30	$85.30	$85.30
Purchase #7	$156.74	7.733%	$168.8607	$168.86	$168.85	$168.90
7 purchase totals =	$745.51		$810.6832	$810.68	$810.65	$810.70