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	$202.37	8.110%	$218.7822	$218.78	$218.80	$218.80
Purchase #2	$65.28	8.481%	$70.8164	$70.82	$70.80	$70.80
Purchase #3	$150.80	5.344%	$158.8588	$158.86	$158.85	$158.90
Purchase #4	$71.97	13.204%	$81.4729	$81.47	$81.45	$81.50
Purchase #5	$151.39	4.250%	$157.8241	$157.82	$157.80	$157.80
Purchase #6	$56.85	4.553%	$59.4384	$59.44	$59.45	$59.40
Purchase #7	$234.48	13.134%	$265.2766	$265.28	$265.30	$265.30
7 purchase totals =	$933.14		$1,012.4694	$1,012.47	$1,012.45	$1,012.50