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	$83.88	7.246%	$89.9579	$89.96	$89.95	$90.00
Purchase #2	$95.28	8.515%	$103.3931	$103.39	$103.40	$103.40
Purchase #3	$73.65	11.408%	$82.052	$82.05	$82.05	$82.10
Purchase #4	$38.65	5.727%	$40.8635	$40.86	$40.85	$40.90
Purchase #5	$132.84	3.473%	$137.4535	$137.45	$137.45	$137.50
Purchase #6	$112.84	11.812%	$126.1687	$126.17	$126.15	$126.20
Purchase #7	$93.31	6.331%	$99.2175	$99.22	$99.20	$99.20
7 purchase totals =	$630.45		$679.1062	$679.10	$679.05	$679.30