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	$236.47	8.518%	$256.6125	$256.61	$256.60	$256.60
Purchase #2	$63.33	6.155%	$67.228	$67.23	$67.25	$67.20
Purchase #3	$152.56	4.783%	$159.8569	$159.86	$159.85	$159.90
Purchase #4	$78.45	3.287%	$81.0287	$81.03	$81.05	$81.00
Purchase #5	$102.82	8.233%	$111.2852	$111.29	$111.30	$111.30
Purchase #6	$160.70	5.658%	$169.7924	$169.79	$169.80	$169.80
Purchase #7	$48.94	3.197%	$50.5046	$50.50	$50.50	$50.50
7 purchase totals =	$843.27		$896.3083	$896.31	$896.35	$896.30