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	$87.30	13.639%	$99.2068	$99.21	$99.20	$99.20
Purchase #2	$91.52	13.455%	$103.834	$103.83	$103.85	$103.80
Purchase #3	$123.71	12.803%	$139.5486	$139.55	$139.55	$139.50
Purchase #4	$56.40	11.105%	$62.6632	$62.66	$62.65	$62.70
Purchase #5	$89.90	5.765%	$95.0827	$95.08	$95.10	$95.10
Purchase #6	$42.94	5.254%	$45.1961	$45.20	$45.20	$45.20
Purchase #7	$144.70	9.671%	$158.6939	$158.69	$158.70	$158.70
7 purchase totals =	$636.47		$704.2253	$704.22	$704.25	$704.20