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	$216.37	4.246%	$225.5571	$225.56	$225.55	$225.60
Purchase #2	$250.60	3.119%	$258.4162	$258.42	$258.40	$258.40
Purchase #3	$114.87	7.229%	$123.174	$123.17	$123.15	$123.20
Purchase #4	$177.67	6.685%	$189.5472	$189.55	$189.55	$189.50
Purchase #5	$38.27	4.472%	$39.9814	$39.98	$40.00	$40.00
Purchase #6	$114.64	6.378%	$121.9517	$121.95	$121.95	$122.00
Purchase #7	$41.81	8.206%	$45.2409	$45.24	$45.25	$45.20
7 purchase totals =	$954.23		$1,003.8685	$1,003.87	$1,003.85	$1,003.90