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	$90.67	10.144%	$99.8676	$99.87	$99.85	$99.90
Purchase #2	$91.39	7.438%	$98.1876	$98.19	$98.20	$98.20
Purchase #3	$69.37	4.761%	$72.6727	$72.67	$72.65	$72.70
Purchase #4	$132.28	11.445%	$147.4194	$147.42	$147.40	$147.40
Purchase #5	$48.97	5.108%	$51.4714	$51.47	$51.45	$51.50
Purchase #6	$152.87	3.142%	$157.6732	$157.67	$157.65	$157.70
Purchase #7	$146.35	5.645%	$154.6115	$154.61	$154.60	$154.60
7 purchase totals =	$731.90		$781.9034	$781.90	$781.80	$782.00