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	$80.43	10.826%	$89.1374	$89.14	$89.15	$89.10
Purchase #2	$182.75	8.553%	$198.3806	$198.38	$198.40	$198.40
Purchase #3	$51.90	4.711%	$54.345	$54.35	$54.35	$54.30
Purchase #4	$26.43	9.475%	$28.9342	$28.93	$28.95	$28.90
Purchase #5	$176.74	13.185%	$200.0432	$200.04	$200.05	$200.00
Purchase #6	$240.88	5.357%	$253.7839	$253.78	$253.80	$253.80
Purchase #7	$32.40	3.306%	$33.4711	$33.47	$33.45	$33.50
7 purchase totals =	$791.53		$858.0954	$858.09	$858.15	$858.00