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	$128.31	6.779%	$137.0081	$137.01	$137.00	$137.00
Purchase #2	$41.74	4.229%	$43.5052	$43.51	$43.50	$43.50
Purchase #3	$248.46	3.177%	$256.3536	$256.35	$256.35	$256.40
Purchase #4	$10.92	11.340%	$12.1583	$12.16	$12.15	$12.20
Purchase #5	$138.57	10.529%	$153.16	$153.16	$153.15	$153.20
Purchase #6	$17.76	13.768%	$20.2052	$20.21	$20.20	$20.20
Purchase #7	$184.31	7.617%	$198.3489	$198.35	$198.35	$198.30
7 purchase totals =	$770.07		$820.7393	$820.75	$820.70	$820.80