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	$63.42	9.600%	$69.5083	$69.51	$69.50	$69.50
Purchase #2	$111.57	6.479%	$118.7986	$118.80	$118.80	$118.80
Purchase #3	$175.71	13.471%	$199.3799	$199.38	$199.40	$199.40
Purchase #4	$80.61	12.671%	$90.8241	$90.82	$90.80	$90.80
Purchase #5	$67.58	12.535%	$76.0512	$76.05	$76.05	$76.10
Purchase #6	$9.35	13.331%	$10.5964	$10.60	$10.60	$10.60
Purchase #7	$96.45	5.777%	$102.0219	$102.02	$102.00	$102.00
7 purchase totals =	$604.69		$667.1804	$667.18	$667.15	$667.20