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	$33.53	3.188%	$34.5989	$34.60	$34.60	$34.60
Purchase #2	$156.90	8.108%	$169.6215	$169.62	$169.60	$169.60
Purchase #3	$138.96	9.306%	$151.8916	$151.89	$151.90	$151.90
Purchase #4	$139.59	4.669%	$146.1075	$146.11	$146.10	$146.10
Purchase #5	$111.71	10.398%	$123.3256	$123.33	$123.35	$123.30
Purchase #6	$205.45	10.425%	$226.8682	$226.87	$226.85	$226.90
Purchase #7	$66.71	5.553%	$70.4144	$70.41	$70.40	$70.40
7 purchase totals =	$852.85		$922.8277	$922.83	$922.80	$922.80