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	$248.83	9.159%	$271.6203	$271.62	$271.60	$271.60
Purchase #2	$61.72	5.755%	$65.272	$65.27	$65.25	$65.30
Purchase #3	$80.62	11.431%	$89.8357	$89.84	$89.85	$89.80
Purchase #4	$45.54	4.246%	$47.4736	$47.47	$47.45	$47.50
Purchase #5	$230.43	12.111%	$258.3374	$258.34	$258.35	$258.30
Purchase #6	$221.43	9.252%	$241.9167	$241.92	$241.90	$241.90
Purchase #7	$206.52	3.852%	$214.4752	$214.48	$214.50	$214.50
7 purchase totals =	$1,095.09		$1,188.9309	$1,188.94	$1,188.90	$1,188.90