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	$129.39	5.253%	$136.1869	$136.19	$136.20	$136.20
Purchase #2	$155.63	3.157%	$160.5432	$160.54	$160.55	$160.50
Purchase #3	$175.66	3.297%	$181.4515	$181.45	$181.45	$181.50
Purchase #4	$131.47	5.629%	$138.8704	$138.87	$138.85	$138.90
Purchase #5	$227.64	6.329%	$242.0473	$242.05	$242.05	$242.00
Purchase #6	$47.55	12.677%	$53.5779	$53.58	$53.60	$53.60
Purchase #7	$233.27	9.440%	$255.2907	$255.29	$255.30	$255.30
7 purchase totals =	$1,100.61		$1,167.9679	$1,167.97	$1,168.00	$1,168.00