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	$85.78	5.346%	$90.3658	$90.37	$90.35	$90.40
Purchase #2	$40.68	11.133%	$45.2089	$45.21	$45.20	$45.20
Purchase #3	$121.28	9.431%	$132.7179	$132.72	$132.70	$132.70
Purchase #4	$94.82	10.826%	$105.0852	$105.09	$105.10	$105.10
Purchase #5	$174.58	9.743%	$191.5893	$191.59	$191.60	$191.60
Purchase #6	$80.32	7.689%	$86.4958	$86.50	$86.50	$86.50
Purchase #7	$237.49	11.827%	$265.5779	$265.58	$265.60	$265.60
7 purchase totals =	$834.95		$917.0408	$917.06	$917.05	$917.10