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	$229.70	12.706%	$258.8857	$258.89	$258.90	$258.90
Purchase #2	$89.86	5.162%	$94.4986	$94.50	$94.50	$94.50
Purchase #3	$55.72	13.745%	$63.3787	$63.38	$63.40	$63.40
Purchase #4	$217.51	13.339%	$246.5237	$246.52	$246.50	$246.50
Purchase #5	$121.34	13.404%	$137.6044	$137.60	$137.60	$137.60
Purchase #6	$212.80	4.755%	$222.9186	$222.92	$222.90	$222.90
Purchase #7	$208.26	5.359%	$219.4207	$219.42	$219.40	$219.40
7 purchase totals =	$1,135.19		$1,243.2304	$1,243.23	$1,243.20	$1,243.20