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	$247.76	5.516%	$261.4264	$261.43	$261.45	$261.40
Purchase #2	$179.61	5.218%	$188.982	$188.98	$189.00	$189.00
Purchase #3	$248.52	3.566%	$257.3822	$257.38	$257.40	$257.40
Purchase #4	$233.59	9.533%	$255.8581	$255.86	$255.85	$255.90
Purchase #5	$45.97	13.704%	$52.2697	$52.27	$52.25	$52.30
Purchase #6	$211.66	6.596%	$225.6211	$225.62	$225.60	$225.60
Purchase #7	$96.53	6.771%	$103.066	$103.07	$103.05	$103.10
7 purchase totals =	$1,263.64		$1,344.6055	$1,344.61	$1,344.60	$1,344.70