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	$193.34	13.224%	$218.9073	$218.91	$218.90	$218.90
Purchase #2	$90.50	13.327%	$102.5609	$102.56	$102.55	$102.60
Purchase #3	$135.52	13.622%	$153.9805	$153.98	$154.00	$154.00
Purchase #4	$57.38	6.147%	$60.9071	$60.91	$60.90	$60.90
Purchase #5	$136.32	6.274%	$144.8727	$144.87	$144.85	$144.90
Purchase #6	$78.42	3.773%	$81.3788	$81.38	$81.40	$81.40
Purchase #7	$9.73	8.342%	$10.5417	$10.54	$10.55	$10.50
7 purchase totals =	$701.21		$773.1490	$773.15	$773.15	$773.20