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	$40.72	6.705%	$43.4503	$43.45	$43.45	$43.50
Purchase #2	$220.88	9.320%	$241.466	$241.47	$241.45	$241.50
Purchase #3	$209.78	5.631%	$221.5927	$221.59	$221.60	$221.60
Purchase #4	$119.59	8.229%	$129.4311	$129.43	$129.45	$129.40
Purchase #5	$38.28	6.554%	$40.7889	$40.79	$40.80	$40.80
Purchase #6	$163.45	3.127%	$168.5611	$168.56	$168.55	$168.60
Purchase #7	$113.47	13.846%	$129.1811	$129.18	$129.20	$129.20
7 purchase totals =	$906.17		$974.4712	$974.47	$974.50	$974.60