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	$46.47	13.160%	$52.5855	$52.59	$52.60	$52.60
Purchase #2	$248.99	4.789%	$260.9141	$260.91	$260.90	$260.90
Purchase #3	$49.48	10.331%	$54.5918	$54.59	$54.60	$54.60
Purchase #4	$240.46	12.541%	$270.6161	$270.62	$270.60	$270.60
Purchase #5	$200.32	10.554%	$221.4618	$221.46	$221.45	$221.50
Purchase #6	$164.52	12.608%	$185.2627	$185.26	$185.25	$185.30
Purchase #7	$24.99	3.736%	$25.9236	$25.92	$25.90	$25.90
7 purchase totals =	$975.23		$1,071.3556	$1,071.35	$1,071.30	$1,071.40