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	$122.44	4.178%	$127.5555	$127.56	$127.55	$127.60
Purchase #2	$78.92	13.344%	$89.4511	$89.45	$89.45	$89.50
Purchase #3	$229.71	8.755%	$249.8211	$249.82	$249.80	$249.80
Purchase #4	$181.66	8.321%	$196.7759	$196.78	$196.80	$196.80
Purchase #5	$158.51	12.364%	$178.1082	$178.11	$178.10	$178.10
Purchase #6	$104.34	12.536%	$117.4201	$117.42	$117.40	$117.40
Purchase #7	$108.43	7.299%	$116.3443	$116.34	$116.35	$116.30
7 purchase totals =	$984.01		$1,075.4762	$1,075.48	$1,075.45	$1,075.50