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	$90.32	10.315%	$99.6365	$99.64	$99.65	$99.60
Purchase #2	$79.35	13.218%	$89.8385	$89.84	$89.85	$89.80
Purchase #3	$161.58	10.669%	$178.819	$178.82	$178.80	$178.80
Purchase #4	$105.65	11.763%	$118.0776	$118.08	$118.10	$118.10
Purchase #5	$29.57	3.814%	$30.6978	$30.70	$30.70	$30.70
Purchase #6	$32.40	7.861%	$34.947	$34.95	$34.95	$34.90
Purchase #7	$116.27	13.512%	$131.9804	$131.98	$132.00	$132.00
7 purchase totals =	$615.14		$683.9968	$684.01	$684.05	$683.90