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	$55.63	11.258%	$61.8928	$61.89	$61.90	$61.90
Purchase #2	$83.35	9.123%	$90.954	$90.95	$90.95	$91.00
Purchase #3	$62.51	10.178%	$68.8723	$68.87	$68.85	$68.90
Purchase #4	$113.29	5.579%	$119.6104	$119.61	$119.60	$119.60
Purchase #5	$51.52	7.458%	$55.3624	$55.36	$55.35	$55.40
Purchase #6	$127.56	11.789%	$142.598	$142.60	$142.60	$142.60
Purchase #7	$241.26	8.316%	$261.3232	$261.32	$261.30	$261.30
7 purchase totals =	$735.12		$800.6131	$800.60	$800.55	$800.70