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	$81.31	8.845%	$88.5019	$88.50	$88.50	$88.50
Purchase #2	$149.37	8.463%	$162.0112	$162.01	$162.00	$162.00
Purchase #3	$99.55	10.856%	$110.3571	$110.36	$110.35	$110.40
Purchase #4	$151.39	10.466%	$167.2345	$167.23	$167.25	$167.20
Purchase #5	$248.68	6.794%	$265.5753	$265.58	$265.60	$265.60
Purchase #6	$37.59	13.562%	$42.688	$42.69	$42.70	$42.70
Purchase #7	$18.47	11.117%	$20.5233	$20.52	$20.50	$20.50
7 purchase totals =	$786.36		$856.8913	$856.89	$856.90	$856.90