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	$49.29	4.723%	$51.618	$51.62	$51.60	$51.60
Purchase #2	$132.67	9.734%	$145.5841	$145.58	$145.60	$145.60
Purchase #3	$69.29	4.310%	$72.2764	$72.28	$72.30	$72.30
Purchase #4	$188.26	5.704%	$198.9984	$199.00	$199.00	$199.00
Purchase #5	$89.62	9.266%	$97.9242	$97.92	$97.90	$97.90
Purchase #6	$46.72	12.597%	$52.6053	$52.61	$52.60	$52.60
Purchase #7	$90.49	10.231%	$99.748	$99.75	$99.75	$99.70
7 purchase totals =	$666.34		$718.7544	$718.76	$718.75	$718.70