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	$111.45	7.618%	$119.9403	$119.94	$119.95	$119.90
Purchase #2	$41.27	4.493%	$43.1243	$43.12	$43.10	$43.10
Purchase #3	$124.34	9.793%	$136.5166	$136.52	$136.50	$136.50
Purchase #4	$39.53	13.402%	$44.8278	$44.83	$44.85	$44.80
Purchase #5	$81.60	9.599%	$89.4328	$89.43	$89.45	$89.40
Purchase #6	$75.51	6.183%	$80.1788	$80.18	$80.20	$80.20
Purchase #7	$5.98	6.761%	$6.3843	$6.38	$6.40	$6.40
7 purchase totals =	$479.68		$520.4049	$520.40	$520.45	$520.30