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	$146.28	6.580%	$155.9052	$155.91	$155.90	$155.90
Purchase #2	$38.30	6.366%	$40.7382	$40.74	$40.75	$40.70
Purchase #3	$101.79	5.402%	$107.2887	$107.29	$107.30	$107.30
Purchase #4	$164.53	12.457%	$185.0255	$185.03	$185.05	$185.00
Purchase #5	$12.91	7.346%	$13.8584	$13.86	$13.85	$13.90
Purchase #6	$197.78	7.113%	$211.8481	$211.85	$211.85	$211.80
Purchase #7	$181.93	8.228%	$196.8992	$196.90	$196.90	$196.90
7 purchase totals =	$843.52		$911.5633	$911.58	$911.60	$911.50