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	$244.81	4.569%	$255.9954	$256.00	$256.00	$256.00
Purchase #2	$103.81	11.846%	$116.1073	$116.11	$116.10	$116.10
Purchase #3	$46.48	12.833%	$52.4448	$52.44	$52.45	$52.40
Purchase #4	$239.92	12.518%	$269.9532	$269.95	$269.95	$270.00
Purchase #5	$11.43	12.217%	$12.8264	$12.83	$12.85	$12.80
Purchase #6	$181.96	7.783%	$196.1219	$196.12	$196.10	$196.10
Purchase #7	$9.87	10.657%	$10.9218	$10.92	$10.90	$10.90
7 purchase totals =	$838.28		$914.3708	$914.37	$914.35	$914.30