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	$14.82	10.619%	$16.3937	$16.39	$16.40	$16.40
Purchase #2	$42.97	4.856%	$45.0566	$45.06	$45.05	$45.10
Purchase #3	$12.34	9.118%	$13.4652	$13.47	$13.45	$13.50
Purchase #4	$44.96	6.220%	$47.7565	$47.76	$47.75	$47.80
Purchase #5	$228.69	3.671%	$237.0852	$237.09	$237.10	$237.10
Purchase #6	$105.49	10.427%	$116.4894	$116.49	$116.50	$116.50
Purchase #7	$78.27	5.159%	$82.3079	$82.31	$82.30	$82.30
7 purchase totals =	$527.54		$558.5545	$558.57	$558.55	$558.70