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	$38.48	4.606%	$40.2524	$40.25	$40.25	$40.30
Purchase #2	$161.82	12.385%	$181.8614	$181.86	$181.85	$181.90
Purchase #3	$167.45	11.851%	$187.2945	$187.29	$187.30	$187.30
Purchase #4	$122.89	12.521%	$138.2771	$138.28	$138.30	$138.30
Purchase #5	$248.87	12.677%	$280.4192	$280.42	$280.40	$280.40
Purchase #6	$135.90	6.678%	$144.9754	$144.98	$145.00	$145.00
Purchase #7	$57.82	7.578%	$62.2016	$62.20	$62.20	$62.20
7 purchase totals =	$933.23		$1,035.2816	$1,035.28	$1,035.30	$1,035.40