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	$29.39	9.704%	$32.242	$32.24	$32.25	$32.20
Purchase #2	$148.86	3.839%	$154.5747	$154.57	$154.55	$154.60
Purchase #3	$137.89	10.253%	$152.0279	$152.03	$152.05	$152.00
Purchase #4	$193.36	8.136%	$209.0918	$209.09	$209.10	$209.10
Purchase #5	$131.49	3.522%	$136.1211	$136.12	$136.10	$136.10
Purchase #6	$92.89	4.567%	$97.1323	$97.13	$97.15	$97.10
Purchase #7	$153.25	7.816%	$165.228	$165.23	$165.25	$165.20
7 purchase totals =	$887.13		$946.4178	$946.41	$946.45	$946.30