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	$6.98	9.569%	$7.6479	$7.65	$7.65	$7.60
Purchase #2	$159.52	10.751%	$176.67	$176.67	$176.65	$176.70
Purchase #3	$111.74	10.564%	$123.5442	$123.54	$123.55	$123.50
Purchase #4	$101.37	6.126%	$107.5799	$107.58	$107.60	$107.60
Purchase #5	$81.64	10.612%	$90.3036	$90.30	$90.30	$90.30
Purchase #6	$227.63	11.828%	$254.5541	$254.55	$254.55	$254.60
Purchase #7	$36.68	5.571%	$38.7234	$38.72	$38.70	$38.70
7 purchase totals =	$725.56		$799.0231	$799.01	$799.00	$799.00