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	$173.61	10.172%	$191.2696	$191.27	$191.25	$191.30
Purchase #2	$108.55	12.684%	$122.3185	$122.32	$122.30	$122.30
Purchase #3	$224.30	12.792%	$252.9925	$252.99	$253.00	$253.00
Purchase #4	$123.71	8.260%	$133.9284	$133.93	$133.95	$133.90
Purchase #5	$54.63	3.480%	$56.5311	$56.53	$56.55	$56.50
Purchase #6	$216.28	10.342%	$238.6477	$238.65	$238.65	$238.60
Purchase #7	$81.70	11.141%	$90.8022	$90.80	$90.80	$90.80
7 purchase totals =	$982.78		$1,086.4900	$1,086.49	$1,086.50	$1,086.40