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	$154.75	6.326%	$164.5395	$164.54	$164.55	$164.50
Purchase #2	$70.61	11.803%	$78.9441	$78.94	$78.95	$78.90
Purchase #3	$199.87	5.606%	$211.0747	$211.07	$211.05	$211.10
Purchase #4	$148.71	10.732%	$164.6696	$164.67	$164.65	$164.70
Purchase #5	$63.42	3.581%	$65.6911	$65.69	$65.70	$65.70
Purchase #6	$118.41	4.150%	$123.324	$123.32	$123.30	$123.30
Purchase #7	$13.35	3.663%	$13.839	$13.84	$13.85	$13.80
7 purchase totals =	$769.12		$822.0820	$822.07	$822.05	$822.00