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	$78.50	12.724%	$88.4883	$88.49	$88.50	$88.50
Purchase #2	$206.61	7.561%	$222.2318	$222.23	$222.25	$222.20
Purchase #3	$14.93	8.536%	$16.2044	$16.20	$16.20	$16.20
Purchase #4	$181.35	9.785%	$199.0951	$199.10	$199.10	$199.10
Purchase #5	$70.40	11.584%	$78.5551	$78.56	$78.55	$78.60
Purchase #6	$67.38	7.609%	$72.5069	$72.51	$72.50	$72.50
Purchase #7	$219.58	8.661%	$238.5978	$238.60	$238.60	$238.60
7 purchase totals =	$838.75		$915.6794	$915.69	$915.70	$915.70