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	$70.67	11.644%	$78.8988	$78.90	$78.90	$78.90
Purchase #2	$218.47	4.164%	$227.5671	$227.57	$227.55	$227.60
Purchase #3	$177.38	8.496%	$192.4502	$192.45	$192.45	$192.50
Purchase #4	$160.71	5.721%	$169.9042	$169.90	$169.90	$169.90
Purchase #5	$212.39	6.664%	$226.5437	$226.54	$226.55	$226.50
Purchase #6	$181.89	4.447%	$189.9786	$189.98	$190.00	$190.00
Purchase #7	$132.34	6.163%	$140.4961	$140.50	$140.50	$140.50
7 purchase totals =	$1,153.85		$1,225.8387	$1,225.84	$1,225.85	$1,225.90