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	$228.46	11.446%	$254.6095	$254.61	$254.60	$254.60
Purchase #2	$35.94	11.440%	$40.0515	$40.05	$40.05	$40.10
Purchase #3	$217.36	5.256%	$228.7844	$228.78	$228.80	$228.80
Purchase #4	$122.87	11.131%	$136.5467	$136.55	$136.55	$136.50
Purchase #5	$34.50	7.798%	$37.1903	$37.19	$37.20	$37.20
Purchase #6	$45.52	8.352%	$49.3218	$49.32	$49.30	$49.30
Purchase #7	$188.89	12.155%	$211.8496	$211.85	$211.85	$211.80
7 purchase totals =	$873.54		$958.3538	$958.35	$958.35	$958.30