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	$197.39	6.580%	$210.3783	$210.38	$210.40	$210.40
Purchase #2	$109.27	12.513%	$122.943	$122.94	$122.95	$122.90
Purchase #3	$212.82	8.117%	$230.0946	$230.09	$230.10	$230.10
Purchase #4	$116.82	12.187%	$131.0569	$131.06	$131.05	$131.10
Purchase #5	$144.30	8.264%	$156.225	$156.23	$156.25	$156.20
Purchase #6	$133.37	7.525%	$143.4061	$143.41	$143.40	$143.40
Purchase #7	$92.56	7.448%	$99.4539	$99.45	$99.45	$99.50
7 purchase totals =	$1,006.53		$1,093.5578	$1,093.56	$1,093.60	$1,093.60