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	$240.33	9.790%	$263.8583	$263.86	$263.85	$263.90
Purchase #2	$184.42	6.493%	$196.3944	$196.39	$196.40	$196.40
Purchase #3	$112.75	6.241%	$119.7867	$119.79	$119.80	$119.80
Purchase #4	$123.66	13.221%	$140.0091	$140.01	$140.00	$140.00
Purchase #5	$179.50	10.851%	$198.9775	$198.98	$199.00	$199.00
Purchase #6	$36.53	9.584%	$40.031	$40.03	$40.05	$40.00
Purchase #7	$44.43	9.190%	$48.5131	$48.51	$48.50	$48.50
7 purchase totals =	$921.62		$1,007.5701	$1,007.57	$1,007.60	$1,007.60