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	$77.80	6.441%	$82.8111	$82.81	$82.80	$82.80
Purchase #2	$84.30	6.752%	$89.9919	$89.99	$90.00	$90.00
Purchase #3	$139.53	12.109%	$156.4257	$156.43	$156.45	$156.40
Purchase #4	$43.51	9.501%	$47.6439	$47.64	$47.65	$47.60
Purchase #5	$237.98	11.601%	$265.5881	$265.59	$265.60	$265.60
Purchase #6	$203.97	6.670%	$217.5748	$217.57	$217.55	$217.60
Purchase #7	$44.74	12.293%	$50.2399	$50.24	$50.25	$50.20
7 purchase totals =	$831.83		$910.2754	$910.27	$910.30	$910.20