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	$212.34	6.147%	$225.3925	$225.39	$225.40	$225.40
Purchase #2	$150.69	12.105%	$168.931	$168.93	$168.95	$168.90
Purchase #3	$151.85	8.563%	$164.8529	$164.85	$164.85	$164.90
Purchase #4	$18.43	5.623%	$19.4663	$19.47	$19.45	$19.50
Purchase #5	$169.51	5.758%	$179.2704	$179.27	$179.25	$179.30
Purchase #6	$205.92	11.126%	$228.8307	$228.83	$228.85	$228.80
Purchase #7	$95.84	9.564%	$105.0061	$105.01	$105.00	$105.00
7 purchase totals =	$1,004.58		$1,091.7499	$1,091.75	$1,091.75	$1,091.80