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	$82.30	11.665%	$91.9003	$91.90	$91.90	$91.90
Purchase #2	$144.52	6.372%	$153.7288	$153.73	$153.75	$153.70
Purchase #3	$151.92	6.196%	$161.333	$161.33	$161.35	$161.30
Purchase #4	$141.50	9.151%	$154.4487	$154.45	$154.45	$154.40
Purchase #5	$108.80	8.118%	$117.6324	$117.63	$117.65	$117.60
Purchase #6	$79.85	10.245%	$88.0306	$88.03	$88.05	$88.00
Purchase #7	$112.96	9.328%	$123.4969	$123.50	$123.50	$123.50
7 purchase totals =	$821.85		$890.5707	$890.57	$890.65	$890.40