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	$219.31	12.535%	$246.8005	$246.80	$246.80	$246.80
Purchase #2	$87.74	3.214%	$90.56	$90.56	$90.55	$90.60
Purchase #3	$19.40	8.560%	$21.0606	$21.06	$21.05	$21.10
Purchase #4	$11.84	5.555%	$12.4977	$12.50	$12.50	$12.50
Purchase #5	$179.93	11.628%	$200.8523	$200.85	$200.85	$200.90
Purchase #6	$31.77	8.786%	$34.5613	$34.56	$34.55	$34.60
Purchase #7	$57.35	7.282%	$61.5262	$61.53	$61.55	$61.50
7 purchase totals =	$607.34		$667.8586	$667.86	$667.85	$668.00