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	$132.32	6.337%	$140.7051	$140.71	$140.70	$140.70
Purchase #2	$52.78	12.337%	$59.2915	$59.29	$59.30	$59.30
Purchase #3	$96.73	7.338%	$103.828	$103.83	$103.85	$103.80
Purchase #4	$90.91	11.637%	$101.4892	$101.49	$101.50	$101.50
Purchase #5	$199.38	11.558%	$222.4243	$222.42	$222.40	$222.40
Purchase #6	$20.35	6.260%	$21.6239	$21.62	$21.60	$21.60
Purchase #7	$71.91	12.721%	$81.0577	$81.06	$81.05	$81.10
7 purchase totals =	$664.38		$730.4197	$730.42	$730.40	$730.40