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	$104.41	6.794%	$111.5036	$111.50	$111.50	$111.50
Purchase #2	$199.94	8.840%	$217.6147	$217.61	$217.60	$217.60
Purchase #3	$242.60	8.242%	$262.5951	$262.60	$262.60	$262.60
Purchase #4	$213.92	8.112%	$231.2732	$231.27	$231.25	$231.30
Purchase #5	$159.30	12.715%	$179.555	$179.56	$179.55	$179.60
Purchase #6	$246.51	10.539%	$272.4897	$272.49	$272.50	$272.50
Purchase #7	$210.25	8.212%	$227.5157	$227.52	$227.50	$227.50
7 purchase totals =	$1,376.93		$1,502.5470	$1,502.55	$1,502.50	$1,502.60