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	$29.42	7.565%	$31.6456	$31.65	$31.65	$31.60
Purchase #2	$52.81	3.808%	$54.821	$54.82	$54.80	$54.80
Purchase #3	$51.77	9.779%	$56.8326	$56.83	$56.85	$56.80
Purchase #4	$109.61	3.173%	$113.0879	$113.09	$113.10	$113.10
Purchase #5	$85.43	5.406%	$90.0483	$90.05	$90.05	$90.00
Purchase #6	$139.45	6.480%	$148.4864	$148.49	$148.50	$148.50
Purchase #7	$130.66	8.310%	$141.5178	$141.52	$141.50	$141.50
7 purchase totals =	$599.15		$636.4396	$636.45	$636.45	$636.30