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	$91.32	3.284%	$94.3189	$94.32	$94.30	$94.30
Purchase #2	$224.26	4.595%	$234.5647	$234.56	$234.55	$234.60
Purchase #3	$177.50	11.538%	$197.98	$197.98	$198.00	$198.00
Purchase #4	$100.56	10.617%	$111.2365	$111.24	$111.25	$111.20
Purchase #5	$38.32	5.393%	$40.3866	$40.39	$40.40	$40.40
Purchase #6	$126.51	10.239%	$139.4634	$139.46	$139.45	$139.50
Purchase #7	$141.79	7.499%	$152.4228	$152.42	$152.40	$152.40
7 purchase totals =	$900.26		$970.3729	$970.37	$970.35	$970.40