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	$158.97	8.782%	$172.9307	$172.93	$172.95	$172.90
Purchase #2	$186.77	5.122%	$196.3364	$196.34	$196.35	$196.30
Purchase #3	$30.67	13.597%	$34.8402	$34.84	$34.85	$34.80
Purchase #4	$100.65	13.138%	$113.8734	$113.87	$113.85	$113.90
Purchase #5	$230.43	8.121%	$249.1432	$249.14	$249.15	$249.10
Purchase #6	$32.83	6.175%	$34.8573	$34.86	$34.85	$34.90
Purchase #7	$50.39	6.182%	$53.5051	$53.51	$53.50	$53.50
7 purchase totals =	$790.71		$855.4863	$855.49	$855.50	$855.40