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	$9.97	13.169%	$11.2829	$11.28	$11.30	$11.30
Purchase #2	$99.28	10.305%	$109.5108	$109.51	$109.50	$109.50
Purchase #3	$213.51	11.423%	$237.8992	$237.90	$237.90	$237.90
Purchase #4	$109.28	10.163%	$120.3861	$120.39	$120.40	$120.40
Purchase #5	$234.54	7.869%	$252.996	$253.00	$253.00	$253.00
Purchase #6	$24.86	11.796%	$27.7925	$27.79	$27.80	$27.80
Purchase #7	$190.85	3.183%	$196.9248	$196.92	$196.90	$196.90
7 purchase totals =	$882.29		$956.7923	$956.79	$956.80	$956.80