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	$38.90	5.114%	$40.8893	$40.89	$40.90	$40.90
Purchase #2	$205.55	8.474%	$222.9683	$222.97	$222.95	$223.00
Purchase #3	$193.49	13.127%	$218.8894	$218.89	$218.90	$218.90
Purchase #4	$6.32	4.390%	$6.5974	$6.60	$6.60	$6.60
Purchase #5	$48.43	11.137%	$53.8236	$53.82	$53.80	$53.80
Purchase #6	$42.62	13.653%	$48.4389	$48.44	$48.45	$48.40
Purchase #7	$218.95	13.596%	$248.7184	$248.72	$248.70	$248.70
7 purchase totals =	$754.26		$840.3253	$840.33	$840.30	$840.30