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	$47.79	6.365%	$50.8318	$50.83	$50.85	$50.80
Purchase #2	$127.90	12.802%	$144.2738	$144.27	$144.25	$144.30
Purchase #3	$170.97	12.692%	$192.6695	$192.67	$192.65	$192.70
Purchase #4	$121.26	4.757%	$127.0283	$127.03	$127.05	$127.00
Purchase #5	$98.34	13.836%	$111.9463	$111.95	$111.95	$111.90
Purchase #6	$110.32	7.137%	$118.1935	$118.19	$118.20	$118.20
Purchase #7	$44.52	3.213%	$45.9504	$45.95	$45.95	$46.00
7 purchase totals =	$721.10		$790.8936	$790.89	$790.90	$790.90