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	$242.76	3.512%	$251.2857	$251.29	$251.30	$251.30
Purchase #2	$173.44	6.649%	$184.972	$184.97	$184.95	$185.00
Purchase #3	$101.37	10.863%	$112.3818	$112.38	$112.40	$112.40
Purchase #4	$205.78	3.318%	$212.6078	$212.61	$212.60	$212.60
Purchase #5	$39.49	7.826%	$42.5805	$42.58	$42.60	$42.60
Purchase #6	$82.88	13.151%	$93.7795	$93.78	$93.80	$93.80
Purchase #7	$185.66	8.172%	$200.8321	$200.83	$200.85	$200.80
7 purchase totals =	$1,031.38		$1,098.4394	$1,098.44	$1,098.50	$1,098.50