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	$220.88	6.360%	$234.928	$234.93	$234.95	$234.90
Purchase #2	$164.72	10.317%	$181.7142	$181.71	$181.70	$181.70
Purchase #3	$215.83	13.153%	$244.2181	$244.22	$244.20	$244.20
Purchase #4	$131.32	4.256%	$136.909	$136.91	$136.90	$136.90
Purchase #5	$121.56	12.836%	$137.1634	$137.16	$137.15	$137.20
Purchase #6	$46.97	4.486%	$49.0771	$49.08	$49.10	$49.10
Purchase #7	$182.90	7.609%	$196.8169	$196.82	$196.80	$196.80
7 purchase totals =	$1,084.18		$1,180.8267	$1,180.83	$1,180.80	$1,180.80