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	$50.58	10.279%	$55.7791	$55.78	$55.80	$55.80
Purchase #2	$175.73	4.348%	$183.3707	$183.37	$183.35	$183.40
Purchase #3	$142.72	11.262%	$158.7931	$158.79	$158.80	$158.80
Purchase #4	$240.90	7.493%	$258.9506	$258.95	$258.95	$259.00
Purchase #5	$60.45	12.729%	$68.1447	$68.14	$68.15	$68.10
Purchase #6	$131.75	6.120%	$139.8131	$139.81	$139.80	$139.80
Purchase #7	$141.89	6.250%	$150.7581	$150.76	$150.75	$150.80
7 purchase totals =	$944.02		$1,015.6094	$1,015.60	$1,015.60	$1,015.70