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	$41.31	3.593%	$42.7943	$42.79	$42.80	$42.80
Purchase #2	$46.88	5.206%	$49.3206	$49.32	$49.30	$49.30
Purchase #3	$173.33	9.746%	$190.2227	$190.22	$190.20	$190.20
Purchase #4	$128.93	11.561%	$143.8356	$143.84	$143.85	$143.80
Purchase #5	$32.65	5.727%	$34.5199	$34.52	$34.50	$34.50
Purchase #6	$232.59	12.254%	$261.0916	$261.09	$261.10	$261.10
Purchase #7	$108.39	11.141%	$120.4657	$120.47	$120.45	$120.50
7 purchase totals =	$764.08		$842.2504	$842.25	$842.20	$842.20