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	$119.74	10.502%	$132.3151	$132.32	$132.30	$132.30
Purchase #2	$59.58	10.529%	$65.8532	$65.85	$65.85	$65.90
Purchase #3	$149.35	3.420%	$154.4578	$154.46	$154.45	$154.50
Purchase #4	$49.26	12.372%	$55.3544	$55.35	$55.35	$55.40
Purchase #5	$244.83	12.666%	$275.8402	$275.84	$275.85	$275.80
Purchase #6	$213.82	11.680%	$238.7942	$238.79	$238.80	$238.80
Purchase #7	$62.31	6.440%	$66.3228	$66.32	$66.30	$66.30
7 purchase totals =	$898.89		$988.9377	$988.93	$988.90	$989.00