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	$89.41	12.206%	$100.3234	$100.32	$100.30	$100.30
Purchase #2	$201.41	11.526%	$224.6245	$224.62	$224.60	$224.60
Purchase #3	$112.89	3.310%	$116.6267	$116.63	$116.65	$116.60
Purchase #4	$94.92	8.331%	$102.8278	$102.83	$102.85	$102.80
Purchase #5	$173.43	9.360%	$189.663	$189.66	$189.65	$189.70
Purchase #6	$90.85	10.547%	$100.4319	$100.43	$100.45	$100.40
Purchase #7	$49.32	10.187%	$54.3442	$54.34	$54.35	$54.30
7 purchase totals =	$812.23		$888.8415	$888.83	$888.85	$888.70