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	$15.52	3.488%	$16.0613	$16.06	$16.05	$16.10
Purchase #2	$250.87	9.384%	$274.4116	$274.41	$274.40	$274.40
Purchase #3	$90.62	13.319%	$102.6897	$102.69	$102.70	$102.70
Purchase #4	$185.83	7.611%	$199.9735	$199.97	$199.95	$200.00
Purchase #5	$146.52	10.658%	$162.1361	$162.14	$162.15	$162.10
Purchase #6	$40.93	4.107%	$42.611	$42.61	$42.60	$42.60
Purchase #7	$106.34	10.579%	$117.5897	$117.59	$117.60	$117.60
7 purchase totals =	$836.63		$915.4729	$915.47	$915.45	$915.50