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	$80.78	11.764%	$90.283	$90.28	$90.30	$90.30
Purchase #2	$19.69	10.284%	$21.7149	$21.71	$21.70	$21.70
Purchase #3	$34.64	6.533%	$36.903	$36.90	$36.90	$36.90
Purchase #4	$198.63	11.587%	$221.6453	$221.65	$221.65	$221.60
Purchase #5	$153.82	9.818%	$168.922	$168.92	$168.90	$168.90
Purchase #6	$144.80	6.137%	$153.6864	$153.69	$153.70	$153.70
Purchase #7	$140.54	9.397%	$153.7465	$153.75	$153.75	$153.70
7 purchase totals =	$772.90		$846.9011	$846.90	$846.90	$846.80