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	$28.42	13.733%	$32.3229	$32.32	$32.30	$32.30
Purchase #2	$167.55	12.499%	$188.4921	$188.49	$188.50	$188.50
Purchase #3	$9.29	6.210%	$9.8669	$9.87	$9.85	$9.90
Purchase #4	$38.86	4.755%	$40.7078	$40.71	$40.70	$40.70
Purchase #5	$64.96	10.726%	$71.9276	$71.93	$71.95	$71.90
Purchase #6	$131.37	5.848%	$139.0525	$139.05	$139.05	$139.10
Purchase #7	$88.40	12.635%	$99.5693	$99.57	$99.55	$99.60
7 purchase totals =	$528.85		$581.9391	$581.94	$581.90	$582.00