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	$105.72	12.348%	$118.7743	$118.77	$118.75	$118.80
Purchase #2	$109.30	7.506%	$117.5041	$117.50	$117.50	$117.50
Purchase #3	$19.32	11.816%	$21.6029	$21.60	$21.60	$21.60
Purchase #4	$211.38	5.291%	$222.5641	$222.56	$222.55	$222.60
Purchase #5	$49.65	5.359%	$52.3107	$52.31	$52.30	$52.30
Purchase #6	$148.79	13.445%	$168.7948	$168.79	$168.80	$168.80
Purchase #7	$114.45	7.464%	$122.9925	$122.99	$123.00	$123.00
7 purchase totals =	$758.61		$824.5434	$824.52	$824.50	$824.60