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	$233.40	8.211%	$252.5645	$252.56	$252.55	$252.60
Purchase #2	$111.82	13.456%	$126.8665	$126.87	$126.85	$126.90
Purchase #3	$47.54	6.560%	$50.6586	$50.66	$50.65	$50.70
Purchase #4	$136.89	4.404%	$142.9186	$142.92	$142.90	$142.90
Purchase #5	$32.67	11.785%	$36.5202	$36.52	$36.50	$36.50
Purchase #6	$182.31	5.461%	$192.2659	$192.27	$192.25	$192.30
Purchase #7	$45.85	8.109%	$49.568	$49.57	$49.55	$49.60
7 purchase totals =	$790.48		$851.3623	$851.37	$851.25	$851.50