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	$89.26	7.320%	$95.7938	$95.79	$95.80	$95.80
Purchase #2	$118.34	8.564%	$128.4746	$128.47	$128.45	$128.50
Purchase #3	$75.81	5.226%	$79.7718	$79.77	$79.75	$79.80
Purchase #4	$56.53	4.684%	$59.1779	$59.18	$59.20	$59.20
Purchase #5	$46.62	11.426%	$51.9468	$51.95	$51.95	$51.90
Purchase #6	$92.61	7.823%	$99.8549	$99.85	$99.85	$99.90
Purchase #7	$38.69	10.255%	$42.6577	$42.66	$42.65	$42.70
7 purchase totals =	$517.86		$557.6775	$557.67	$557.65	$557.80