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	$38.53	12.641%	$43.4006	$43.40	$43.40	$43.40
Purchase #2	$100.37	5.443%	$105.8331	$105.83	$105.85	$105.80
Purchase #3	$167.80	10.767%	$185.867	$185.87	$185.85	$185.90
Purchase #4	$87.41	10.823%	$96.8704	$96.87	$96.85	$96.90
Purchase #5	$210.27	9.543%	$230.3361	$230.34	$230.35	$230.30
Purchase #6	$82.41	10.378%	$90.9625	$90.96	$90.95	$91.00
Purchase #7	$126.59	13.167%	$143.2581	$143.26	$143.25	$143.30
7 purchase totals =	$813.38		$896.5278	$896.53	$896.50	$896.60