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	$29.89	8.672%	$32.4821	$32.48	$32.50	$32.50
Purchase #2	$9.46	11.464%	$10.5445	$10.54	$10.55	$10.50
Purchase #3	$109.78	6.132%	$116.5117	$116.51	$116.50	$116.50
Purchase #4	$16.82	9.248%	$18.3755	$18.38	$18.40	$18.40
Purchase #5	$93.92	6.605%	$100.1234	$100.12	$100.10	$100.10
Purchase #6	$248.71	10.476%	$274.7649	$274.76	$274.75	$274.80
Purchase #7	$16.32	8.203%	$17.6587	$17.66	$17.65	$17.70
7 purchase totals =	$524.90		$570.4608	$570.45	$570.45	$570.50