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	$238.46	13.712%	$271.1576	$271.16	$271.15	$271.20
Purchase #2	$193.71	12.801%	$218.5068	$218.51	$218.50	$218.50
Purchase #3	$29.98	8.714%	$32.5925	$32.59	$32.60	$32.60
Purchase #4	$68.81	4.324%	$71.7853	$71.79	$71.80	$71.80
Purchase #5	$110.27	4.238%	$114.9432	$114.94	$114.95	$114.90
Purchase #6	$141.71	11.503%	$158.0109	$158.01	$158.00	$158.00
Purchase #7	$29.53	10.602%	$32.6608	$32.66	$32.65	$32.70
7 purchase totals =	$812.47		$899.6571	$899.66	$899.65	$899.70