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	$222.88	3.411%	$230.4824	$230.48	$230.50	$230.50
Purchase #2	$96.68	7.373%	$103.8082	$103.81	$103.80	$103.80
Purchase #3	$185.63	13.841%	$211.323	$211.32	$211.30	$211.30
Purchase #4	$104.47	7.680%	$112.4933	$112.49	$112.50	$112.50
Purchase #5	$43.93	6.860%	$46.9436	$46.94	$46.95	$46.90
Purchase #6	$196.71	12.628%	$221.5505	$221.55	$221.55	$221.60
Purchase #7	$51.91	10.225%	$57.2178	$57.22	$57.20	$57.20
7 purchase totals =	$902.21		$983.8188	$983.81	$983.80	$983.80