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	$131.96	5.334%	$138.9987	$139.00	$139.00	$139.00
Purchase #2	$153.40	4.438%	$160.2079	$160.21	$160.20	$160.20
Purchase #3	$117.98	4.513%	$123.3044	$123.30	$123.30	$123.30
Purchase #4	$10.71	9.623%	$11.7406	$11.74	$11.75	$11.70
Purchase #5	$185.95	10.700%	$205.8467	$205.85	$205.85	$205.80
Purchase #6	$198.46	3.658%	$205.7197	$205.72	$205.70	$205.70
Purchase #7	$229.68	4.658%	$240.3785	$240.38	$240.40	$240.40
7 purchase totals =	$1,028.14		$1,086.1965	$1,086.20	$1,086.20	$1,086.10