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	$34.36	13.183%	$38.8897	$38.89	$38.90	$38.90
Purchase #2	$88.39	10.323%	$97.5145	$97.51	$97.50	$97.50
Purchase #3	$124.78	10.194%	$137.5001	$137.50	$137.50	$137.50
Purchase #4	$56.59	9.418%	$61.9196	$61.92	$61.90	$61.90
Purchase #5	$38.49	11.120%	$42.7701	$42.77	$42.75	$42.80
Purchase #6	$149.38	13.499%	$169.5448	$169.54	$169.55	$169.50
Purchase #7	$61.51	8.265%	$66.5938	$66.59	$66.60	$66.60
7 purchase totals =	$553.50		$614.7326	$614.72	$614.70	$614.70