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	$126.93	10.216%	$139.8972	$139.90	$139.90	$139.90
Purchase #2	$129.52	7.466%	$139.19	$139.19	$139.20	$139.20
Purchase #3	$133.65	13.386%	$151.5404	$151.54	$151.55	$151.50
Purchase #4	$125.74	4.540%	$131.4486	$131.45	$131.45	$131.40
Purchase #5	$28.79	7.660%	$30.9953	$31.00	$31.00	$31.00
Purchase #6	$162.87	9.451%	$178.2628	$178.26	$178.25	$178.30
Purchase #7	$36.72	9.610%	$40.2488	$40.25	$40.25	$40.20
7 purchase totals =	$744.22		$811.5831	$811.59	$811.60	$811.50