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	$51.65	7.212%	$55.375	$55.38	$55.40	$55.40
Purchase #2	$144.34	4.309%	$150.5596	$150.56	$150.55	$150.60
Purchase #3	$38.70	13.209%	$43.8119	$43.81	$43.80	$43.80
Purchase #4	$216.69	9.431%	$237.126	$237.13	$237.15	$237.10
Purchase #5	$125.75	9.386%	$137.5529	$137.55	$137.55	$137.60
Purchase #6	$78.43	11.684%	$87.5938	$87.59	$87.60	$87.60
Purchase #7	$81.26	4.752%	$85.1215	$85.12	$85.10	$85.10
7 purchase totals =	$736.82		$797.1407	$797.14	$797.15	$797.20