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	$249.34	10.564%	$275.6803	$275.68	$275.70	$275.70
Purchase #2	$139.99	5.317%	$147.4333	$147.43	$147.45	$147.40
Purchase #3	$18.31	12.314%	$20.5647	$20.56	$20.55	$20.60
Purchase #4	$89.50	9.722%	$98.2012	$98.20	$98.20	$98.20
Purchase #5	$10.89	6.611%	$11.6099	$11.61	$11.60	$11.60
Purchase #6	$42.98	10.141%	$47.3386	$47.34	$47.35	$47.30
Purchase #7	$91.55	10.140%	$100.8332	$100.83	$100.85	$100.80
7 purchase totals =	$642.56		$701.6612	$701.65	$701.70	$701.60