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	$155.87	7.313%	$167.2688	$167.27	$167.25	$167.30
Purchase #2	$141.86	6.117%	$150.5376	$150.54	$150.55	$150.50
Purchase #3	$22.32	5.797%	$23.6139	$23.61	$23.60	$23.60
Purchase #4	$141.98	12.689%	$159.9958	$160.00	$160.00	$160.00
Purchase #5	$109.32	7.504%	$117.5234	$117.52	$117.50	$117.50
Purchase #6	$61.39	9.867%	$67.4474	$67.45	$67.45	$67.40
Purchase #7	$134.95	9.238%	$147.4167	$147.42	$147.40	$147.40
7 purchase totals =	$767.69		$833.8036	$833.81	$833.75	$833.70