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	$31.45	6.624%	$33.5332	$33.53	$33.55	$33.50
Purchase #2	$225.42	13.682%	$256.262	$256.26	$256.25	$256.30
Purchase #3	$40.76	7.488%	$43.8121	$43.81	$43.80	$43.80
Purchase #4	$219.99	8.113%	$237.8378	$237.84	$237.85	$237.80
Purchase #5	$200.26	9.548%	$219.3808	$219.38	$219.40	$219.40
Purchase #6	$190.27	12.552%	$214.1527	$214.15	$214.15	$214.20
Purchase #7	$100.59	3.334%	$103.9437	$103.94	$103.95	$103.90
7 purchase totals =	$1,008.74		$1,108.9223	$1,108.91	$1,108.95	$1,108.90