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	$210.45	9.209%	$229.8303	$229.83	$229.85	$229.80
Purchase #2	$99.80	5.751%	$105.5395	$105.54	$105.55	$105.50
Purchase #3	$115.55	9.474%	$126.4972	$126.50	$126.50	$126.50
Purchase #4	$215.47	4.519%	$225.2071	$225.21	$225.20	$225.20
Purchase #5	$219.37	13.858%	$249.7703	$249.77	$249.75	$249.80
Purchase #6	$27.50	13.614%	$31.2439	$31.24	$31.25	$31.20
Purchase #7	$9.63	7.283%	$10.3314	$10.33	$10.35	$10.30
7 purchase totals =	$897.77		$978.4197	$978.42	$978.45	$978.30