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	$91.43	9.180%	$99.8233	$99.82	$99.80	$99.80
Purchase #2	$231.92	4.574%	$242.528	$242.53	$242.55	$242.50
Purchase #3	$192.29	3.388%	$198.8048	$198.80	$198.80	$198.80
Purchase #4	$51.45	3.481%	$53.241	$53.24	$53.25	$53.20
Purchase #5	$107.93	10.385%	$119.1385	$119.14	$119.15	$119.10
Purchase #6	$183.98	8.444%	$199.5153	$199.52	$199.50	$199.50
Purchase #7	$216.31	9.604%	$237.0844	$237.08	$237.10	$237.10
7 purchase totals =	$1,075.31		$1,150.1353	$1,150.13	$1,150.15	$1,150.00