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	$128.62	8.357%	$139.3688	$139.37	$139.35	$139.40
Purchase #2	$118.77	11.860%	$132.8561	$132.86	$132.85	$132.90
Purchase #3	$50.58	7.404%	$54.3249	$54.32	$54.30	$54.30
Purchase #4	$75.52	7.504%	$81.187	$81.19	$81.20	$81.20
Purchase #5	$40.90	3.651%	$42.3933	$42.39	$42.40	$42.40
Purchase #6	$152.80	6.630%	$162.9306	$162.93	$162.95	$162.90
Purchase #7	$64.74	9.769%	$71.0645	$71.06	$71.05	$71.10
7 purchase totals =	$631.93		$684.1252	$684.12	$684.10	$684.20