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	$99.77	4.825%	$104.5839	$104.58	$104.60	$104.60
Purchase #2	$121.90	5.756%	$128.9166	$128.92	$128.90	$128.90
Purchase #3	$112.76	12.467%	$126.8178	$126.82	$126.80	$126.80
Purchase #4	$90.88	7.450%	$97.6506	$97.65	$97.65	$97.70
Purchase #5	$230.82	12.851%	$260.4827	$260.48	$260.50	$260.50
Purchase #6	$74.34	6.184%	$78.9372	$78.94	$78.95	$78.90
Purchase #7	$207.85	8.291%	$225.0828	$225.08	$225.10	$225.10
7 purchase totals =	$938.32		$1,022.4716	$1,022.47	$1,022.50	$1,022.50