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	$39.28	13.292%	$44.5011	$44.50	$44.50	$44.50
Purchase #2	$112.37	6.489%	$119.6617	$119.66	$119.65	$119.70
Purchase #3	$90.71	3.469%	$93.8567	$93.86	$93.85	$93.90
Purchase #4	$95.82	9.170%	$104.6067	$104.61	$104.60	$104.60
Purchase #5	$31.71	4.554%	$33.1541	$33.15	$33.15	$33.20
Purchase #6	$71.72	9.509%	$78.5399	$78.54	$78.55	$78.50
Purchase #7	$145.49	10.728%	$161.0982	$161.10	$161.10	$161.10
7 purchase totals =	$587.10		$635.4184	$635.42	$635.40	$635.50