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	$104.40	7.564%	$112.2968	$112.30	$112.30	$112.30
Purchase #2	$63.69	10.285%	$70.2405	$70.24	$70.25	$70.20
Purchase #3	$139.37	9.859%	$153.1105	$153.11	$153.10	$153.10
Purchase #4	$155.58	5.665%	$164.3936	$164.39	$164.40	$164.40
Purchase #5	$79.99	13.351%	$90.6695	$90.67	$90.65	$90.70
Purchase #6	$11.27	13.268%	$12.7653	$12.77	$12.75	$12.80
Purchase #7	$173.97	6.857%	$185.8991	$185.90	$185.90	$185.90
7 purchase totals =	$728.27		$789.3753	$789.38	$789.35	$789.40