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	$38.56	13.787%	$43.8763	$43.88	$43.90	$43.90
Purchase #2	$77.37	4.342%	$80.7294	$80.73	$80.75	$80.70
Purchase #3	$92.46	13.432%	$104.8792	$104.88	$104.90	$104.90
Purchase #4	$156.88	5.128%	$164.9248	$164.92	$164.90	$164.90
Purchase #5	$109.82	6.131%	$116.5531	$116.55	$116.55	$116.60
Purchase #6	$153.39	12.464%	$172.5085	$172.51	$172.50	$172.50
Purchase #7	$203.43	8.348%	$220.4123	$220.41	$220.40	$220.40
7 purchase totals =	$831.91		$903.8836	$903.88	$903.90	$903.90