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	$159.86	13.193%	$180.9503	$180.95	$180.95	$181.00
Purchase #2	$32.27	3.178%	$33.2955	$33.30	$33.30	$33.30
Purchase #3	$92.43	8.692%	$100.464	$100.46	$100.45	$100.50
Purchase #4	$119.33	12.780%	$134.5804	$134.58	$134.60	$134.60
Purchase #5	$183.81	4.140%	$191.4197	$191.42	$191.40	$191.40
Purchase #6	$237.89	9.629%	$260.7964	$260.80	$260.80	$260.80
Purchase #7	$86.93	3.363%	$89.8535	$89.85	$89.85	$89.90
7 purchase totals =	$912.52		$991.3598	$991.36	$991.35	$991.50