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	$18.91	5.469%	$19.9442	$19.94	$19.95	$19.90
Purchase #2	$73.52	9.830%	$80.747	$80.75	$80.75	$80.70
Purchase #3	$59.42	3.559%	$61.5348	$61.53	$61.55	$61.50
Purchase #4	$231.82	8.291%	$251.0402	$251.04	$251.05	$251.00
Purchase #5	$82.39	8.507%	$89.3989	$89.40	$89.40	$89.40
Purchase #6	$234.83	6.850%	$250.9159	$250.92	$250.90	$250.90
Purchase #7	$119.93	7.131%	$128.4822	$128.48	$128.50	$128.50
7 purchase totals =	$820.82		$882.0632	$882.06	$882.10	$881.90