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	$19.34	13.245%	$21.9016	$21.90	$21.90	$21.90
Purchase #2	$226.84	12.781%	$255.8324	$255.83	$255.85	$255.80
Purchase #3	$204.46	8.803%	$222.4586	$222.46	$222.45	$222.50
Purchase #4	$65.96	7.269%	$70.7546	$70.75	$70.75	$70.80
Purchase #5	$59.67	9.627%	$65.4144	$65.41	$65.40	$65.40
Purchase #6	$22.31	12.831%	$25.1726	$25.17	$25.15	$25.20
Purchase #7	$218.61	7.509%	$235.0254	$235.03	$235.05	$235.00
7 purchase totals =	$817.19		$896.5596	$896.55	$896.55	$896.60