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	$23.71	4.207%	$24.7075	$24.71	$24.70	$24.70
Purchase #2	$163.65	12.350%	$183.8608	$183.86	$183.85	$183.90
Purchase #3	$137.43	13.135%	$155.4814	$155.48	$155.50	$155.50
Purchase #4	$191.85	10.195%	$211.4091	$211.41	$211.40	$211.40
Purchase #5	$109.66	13.785%	$124.7766	$124.78	$124.80	$124.80
Purchase #6	$196.44	13.752%	$223.4544	$223.45	$223.45	$223.50
Purchase #7	$48.60	12.607%	$54.727	$54.73	$54.75	$54.70
7 purchase totals =	$871.34		$978.4168	$978.42	$978.45	$978.50