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	$94.84	6.143%	$100.666	$100.67	$100.65	$100.70
Purchase #2	$132.71	5.355%	$139.8166	$139.82	$139.80	$139.80
Purchase #3	$16.80	3.199%	$17.3374	$17.34	$17.35	$17.30
Purchase #4	$205.84	8.753%	$223.8572	$223.86	$223.85	$223.90
Purchase #5	$85.78	12.341%	$96.3661	$96.37	$96.35	$96.40
Purchase #6	$106.52	10.716%	$117.9347	$117.93	$117.95	$117.90
Purchase #7	$103.25	8.350%	$111.8714	$111.87	$111.85	$111.90
7 purchase totals =	$745.74		$807.8494	$807.86	$807.80	$807.90