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	$98.52	4.330%	$102.7859	$102.79	$102.80	$102.80
Purchase #2	$100.33	11.728%	$112.0967	$112.10	$112.10	$112.10
Purchase #3	$124.87	11.678%	$139.4523	$139.45	$139.45	$139.50
Purchase #4	$9.46	6.689%	$10.0928	$10.09	$10.10	$10.10
Purchase #5	$77.74	13.854%	$88.5101	$88.51	$88.50	$88.50
Purchase #6	$85.78	5.828%	$90.7793	$90.78	$90.80	$90.80
Purchase #7	$212.26	13.576%	$241.0764	$241.08	$241.10	$241.10
7 purchase totals =	$708.96		$784.7935	$784.80	$784.85	$784.90