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	$246.61	4.593%	$257.9368	$257.94	$257.95	$257.90
Purchase #2	$82.89	10.466%	$91.5653	$91.57	$91.55	$91.60
Purchase #3	$64.76	8.289%	$70.128	$70.13	$70.15	$70.10
Purchase #4	$222.73	3.679%	$230.9242	$230.92	$230.90	$230.90
Purchase #5	$51.57	5.474%	$54.3929	$54.39	$54.40	$54.40
Purchase #6	$104.56	6.747%	$111.6147	$111.61	$111.60	$111.60
Purchase #7	$38.30	9.308%	$41.865	$41.87	$41.85	$41.90
7 purchase totals =	$811.42		$858.4269	$858.43	$858.40	$858.40