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	$25.83	11.760%	$28.8676	$28.87	$28.85	$28.90
Purchase #2	$219.70	8.708%	$238.8315	$238.83	$238.85	$238.80
Purchase #3	$39.80	11.836%	$44.5107	$44.51	$44.50	$44.50
Purchase #4	$81.77	13.273%	$92.6233	$92.62	$92.60	$92.60
Purchase #5	$226.90	6.611%	$241.9004	$241.90	$241.90	$241.90
Purchase #6	$38.92	5.230%	$40.9555	$40.96	$40.95	$41.00
Purchase #7	$225.73	3.533%	$233.705	$233.71	$233.70	$233.70
7 purchase totals =	$858.65		$921.3940	$921.40	$921.35	$921.40