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	$7.97	12.677%	$8.9804	$8.98	$9.00	$9.00
Purchase #2	$249.59	6.517%	$265.8558	$265.86	$265.85	$265.90
Purchase #3	$96.61	9.498%	$105.786	$105.79	$105.80	$105.80
Purchase #4	$86.27	10.741%	$95.5363	$95.54	$95.55	$95.50
Purchase #5	$34.75	6.641%	$37.0577	$37.06	$37.05	$37.10
Purchase #6	$211.45	6.156%	$224.4669	$224.47	$224.45	$224.50
Purchase #7	$58.47	12.116%	$65.5542	$65.55	$65.55	$65.60
7 purchase totals =	$745.11		$803.2373	$803.25	$803.25	$803.40