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	$51.80	10.860%	$57.4255	$57.43	$57.45	$57.40
Purchase #2	$158.90	3.797%	$164.9334	$164.93	$164.95	$164.90
Purchase #3	$9.40	11.812%	$10.5103	$10.51	$10.50	$10.50
Purchase #4	$11.77	4.671%	$12.3198	$12.32	$12.30	$12.30
Purchase #5	$89.55	9.628%	$98.1719	$98.17	$98.15	$98.20
Purchase #6	$190.45	4.300%	$198.6394	$198.64	$198.65	$198.60
Purchase #7	$118.65	7.569%	$127.6306	$127.63	$127.65	$127.60
7 purchase totals =	$630.52		$669.6309	$669.63	$669.65	$669.50