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	$102.61	13.106%	$116.0581	$116.06	$116.05	$116.10
Purchase #2	$18.34	12.571%	$20.6455	$20.65	$20.65	$20.60
Purchase #3	$175.89	13.355%	$199.3801	$199.38	$199.40	$199.40
Purchase #4	$7.89	8.831%	$8.5868	$8.59	$8.60	$8.60
Purchase #5	$174.58	5.565%	$184.2954	$184.30	$184.30	$184.30
Purchase #6	$80.55	11.762%	$90.0243	$90.02	$90.00	$90.00
Purchase #7	$175.49	9.268%	$191.7544	$191.75	$191.75	$191.80
7 purchase totals =	$735.35		$810.7446	$810.75	$810.75	$810.80