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	$179.44	5.634%	$189.5496	$189.55	$189.55	$189.50
Purchase #2	$164.57	5.361%	$173.3926	$173.39	$173.40	$173.40
Purchase #3	$85.36	6.225%	$90.6737	$90.67	$90.65	$90.70
Purchase #4	$198.72	10.436%	$219.4584	$219.46	$219.45	$219.50
Purchase #5	$52.92	6.460%	$56.3386	$56.34	$56.35	$56.30
Purchase #6	$22.67	7.116%	$24.2832	$24.28	$24.30	$24.30
Purchase #7	$162.25	3.632%	$168.1429	$168.14	$168.15	$168.10
7 purchase totals =	$865.93		$921.8390	$921.83	$921.85	$921.80