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	$172.26	5.242%	$181.2899	$181.29	$181.30	$181.30
Purchase #2	$136.43	13.446%	$154.7744	$154.77	$154.75	$154.80
Purchase #3	$188.32	12.492%	$211.8449	$211.84	$211.85	$211.80
Purchase #4	$6.86	10.180%	$7.5583	$7.56	$7.55	$7.60
Purchase #5	$116.60	10.133%	$128.4151	$128.42	$128.40	$128.40
Purchase #6	$75.76	3.665%	$78.5366	$78.54	$78.55	$78.50
Purchase #7	$94.71	13.606%	$107.5962	$107.60	$107.60	$107.60
7 purchase totals =	$790.94		$870.0154	$870.02	$870.00	$870.00