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	$249.60	8.710%	$271.3402	$271.34	$271.35	$271.30
Purchase #2	$13.52	13.241%	$15.3102	$15.31	$15.30	$15.30
Purchase #3	$52.50	5.580%	$55.4295	$55.43	$55.45	$55.40
Purchase #4	$90.28	12.402%	$101.4765	$101.48	$101.50	$101.50
Purchase #5	$182.28	9.462%	$199.5273	$199.53	$199.55	$199.50
Purchase #6	$165.28	4.660%	$172.982	$172.98	$173.00	$173.00
Purchase #7	$42.55	11.611%	$47.4905	$47.49	$47.50	$47.50
7 purchase totals =	$796.01		$863.5562	$863.56	$863.65	$863.50