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	$182.60	9.257%	$199.5033	$199.50	$199.50	$199.50
Purchase #2	$26.62	3.598%	$27.5778	$27.58	$27.60	$27.60
Purchase #3	$90.84	10.457%	$100.3391	$100.34	$100.35	$100.30
Purchase #4	$21.46	6.366%	$22.8261	$22.83	$22.85	$22.80
Purchase #5	$194.65	6.197%	$206.7125	$206.71	$206.70	$206.70
Purchase #6	$31.54	3.149%	$32.5332	$32.53	$32.55	$32.50
Purchase #7	$37.58	13.162%	$42.5263	$42.53	$42.55	$42.50
7 purchase totals =	$585.29		$632.0183	$632.02	$632.10	$631.90