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	$144.27	11.127%	$160.3229	$160.32	$160.30	$160.30
Purchase #2	$156.58	9.806%	$171.9342	$171.93	$171.95	$171.90
Purchase #3	$12.40	9.467%	$13.5739	$13.57	$13.55	$13.60
Purchase #4	$10.67	8.346%	$11.5605	$11.56	$11.55	$11.60
Purchase #5	$58.73	13.304%	$66.5434	$66.54	$66.55	$66.50
Purchase #6	$181.52	3.286%	$187.4847	$187.48	$187.50	$187.50
Purchase #7	$26.48	11.411%	$29.5016	$29.50	$29.50	$29.50
7 purchase totals =	$590.65		$640.9212	$640.90	$640.90	$640.90