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	$86.31	3.715%	$89.5164	$89.52	$89.50	$89.50
Purchase #2	$59.57	9.836%	$65.4293	$65.43	$65.45	$65.40
Purchase #3	$196.82	4.701%	$206.0725	$206.07	$206.05	$206.10
Purchase #4	$221.38	11.567%	$246.987	$246.99	$247.00	$247.00
Purchase #5	$169.69	6.205%	$180.2193	$180.22	$180.20	$180.20
Purchase #6	$120.79	13.415%	$136.994	$136.99	$137.00	$137.00
Purchase #7	$164.84	4.608%	$172.4358	$172.44	$172.45	$172.40
7 purchase totals =	$1,019.40		$1,097.6543	$1,097.66	$1,097.65	$1,097.60